Composition for producing ultraviolet blocking lenses

ABSTRACT

An eyeglass lens forming composition containing light absorbing compounds which may undergo light initiated polymerization is provided. Typically, lens forming compositions that absorb light do not permit enough activating radiation to penetrate into the depths of the lens cavity to adequately initiate polymerization of the lens forming composition. An embodiment of the invention provides a system and method for curing such a lens forming composition to form a lens that does not transmit ultraviolet light. Activating light is used having a wavelength greater than the wavelengths of light which the light absorbing compounds absorb. The power of the formed lenses may be controlled by varying the lens forming conditions. Additionally, the lens forming process may be controlled using a microprocessor based control system.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/395,894 entitled “Method and Composition for Producing UtravioletBlocking Lenses,” filed Sep. 4, 1999, now U.S. Pat. No. 6,712,596, whichis a divisional application of U.S. patent application Ser. No.08/959,973 entitled “Method and Composition for Producing UltravioletBlocking Lenses,” filed on Oct. 29, 1997, now U.S. Pat. No. 5,989,462,which is a continuation-in-part of U.S. patent application Ser. No.08/904,289 entitled “Method and Composition for Producing UltravioletBlocking Lenses” filed on Jul. 31, 1997, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to eyeglass lenses. Moreparticularly, the invention relates to a lens forming composition andmethod for making ultraviolet absorbing plastic lenses by curing thelens forming composition using ultraviolet light.

2. Description of Related Art

It is conventional in the art to produce optical lenses by thermalcuring techniques from the polymer of diethylene glycolbis(allyl)-carbonate (DEG-BAC). In addition, optical lenses may also bemade using ultraviolet (“UV”) light curing techniques. See, for example,U.S. Pat. No. 4,728,469 to Lipscomb et al., U.S. Pat. No. 4,879,318 toLipscomb et al., U.S. Pat. No. 5,364,256 to Lipscomb et al., U.S. Pat.No. 5,415,816 to Buazza et al., U.S. Pat. No. 5,529,728 to Buazza etal., U.S. Pat. No. 5,514,214 to Joel et al., U.S. patent applicationSer. No. 07/425,371 filed Oct. 26, 1989, Ser. No. 08/454,523 filed May30, 1995, Ser. No. 08/453,770 filed May 30, 1995, Ser. No. 07/932,812filed Aug. 18, 1992, Ser. No. 08/636,510 filed Apr. 19, 1996, and U.S.patent application entitled “METHODS AND APPARATUS FOR EYEGLASS LENSCURING USING ULTRAVIOLET LIGHT AND IMPROVED COOLING”—filed Apr. 18,1997, all of which are hereby specifically incorporated by reference.

Curing of a lens by ultraviolet light tends to present certain problemsthat must be overcome to produce a viable lens. Such problems includeyellowing of the lens, cracking of the lens or mold, optical distortionsin the lens, and premature release of the lens from the mold. Inaddition, many of the useful UV-curable lens forming compositionsexhibit certain characteristics which increase the difficulty of a lenscuring process. For example, due to the relatively rapid nature ofultraviolet light initiated reactions, it is a challenge to provide acomposition which is UV curable to form an eyeglass lens. Excessiveexothermic heat tends to cause defects in the cured lens. To avoid suchdefects, the level of photoinitiator may be reduced to levels below whatis customarily employed in the ultraviolet curing art.

While reducing the level of photoinitiator addresses some problems, itmay also cause others. For instance, lowered levels of photoinitiatormay cause the material in regions near an edge of the lens and proximatea gasket wall in a mold cavity to incompletely cure due to the presenceof oxygen in these regions (oxygen is believed to inhibit curing of manylens forming compositions or materials). Uncured lens formingcomposition tends to result in lenses with “wet” edges covered by stickyuncured lens forming composition. Furthermore, uncured lens formingcomposition may migrate to and contaminate the optical surfaces of thelens upon demolding. The contaminated lens is then often unusable.

Uncured lens forming composition has been addressed by a variety ofmethods (see, e.g., the methods described in U.S. Pat. No. 5,529,728 toBuazza et al). Such methods may include removing the gasket and applyingeither an oxygen barrier or a photoinitiator enriched liquid to theexposed edge of the lens, and then re-irradiating the lens with a dosageof ultraviolet light sufficient to completely dry the edge of the lensprior to demolding. During such irradiation, however, higher thandesirable levels of irradiation, or longer than desirable periods ofirradiation, may be required. The additional ultraviolet irradiation mayin some circumstances cause defects such as yellowing in the lens.

The low photoinitiator levels utilized in many ultraviolet curable lensforming compositions may produce a lens which, while fully-cured asmeasured by percentage of remaining double bonds, may not possesssufficient crosslink density on the lens surface to provide desirabledye absorption characteristics during the tinting process.

Various methods of increasing the surface density of such UV curablelenses are described in U.S. Pat. No. 5,529,728 to Buazza et al. In onemethod, the lens is demolded and then the surfaces of the lens areexposed directly to ultraviolet light. The relatively short wavelengths(around 254 nm) provided by some UV sources (e.g., a mercury vapor lamp)tend to cause the material to crosslink quite rapidly. An undesirableeffect of this method, however, is that the lens tends to yellow as aresult of such exposure. Further, any contaminants on the surface of thelens which are exposed to short wavelengths of high intensity UV lightmay cause tint defects.

Another method involves exposing the lens to relatively high intensityultraviolet radiation while it is still within a mold cavity formedbetween glass molds. The glass molds tend to absorb the more effectiveshort wavelengths, while transmitting wavelengths of about 365 nm. Thismethod generally requires long exposure times and often the infraredradiation absorbed by the lens mold assembly will cause prematurerelease of the lens from a mold member. The lens mold assembly may beheated prior to exposure to high intensity ultraviolet light, therebyreducing the amount of radiation necessary to attain a desired level ofcrosslink density. This method, however, is also associated with ahigher rate of premature release.

It is well known in the art that a lens mold/gasket assembly may beheated to cure the lens forming composition from a liquid monomer to asolid polymer. It is also well known that such a lens may be thermallypostcured by applying convective heat to the lens after the molds andgaskets have been removed from the lens.

In this application the terms “lens forming material” and “lens formingcompositions” are used interchangeably.

SUMMARY OF THE INVENTION

One aspect of the invention relates to applying an oxygen barrier aroundthe exposed edges of a lens to initiate the reaction of incompletelycured lens forming material proximate the lens edges. In an embodiment,a liquid polymerizable lens forming composition is placed in a moldcavity having at least two molds and/or a gasket. Ultraviolet rays maybe directed toward at least one of the mold members to substantiallycure the lens forming composition to a lens having material proximatethe edges of the lens that is not fully cured. The gasket may be removedto expose the edges of the lens, and an oxygen barrier comprising aphotoinitiator may be placed around the exposed edges of the lens suchthat at least a portion of the oxygen barrier photoinitiator isproximate lens forming composition that is not fully cured. A portion ofthe incompletely cured material may be removed manually prior to theapplication of the oxygen barrier. Subsequently another set ofultraviolet rays may be directed towards the lens such that at least aportion of the oxygen barrier photoinitiator initiates reaction of lensforming composition while the oxygen barrier substantially preventsoxygen from outside the oxygen barrier from contacting at least aportion of the lens forming composition. The lens may be allowed to cooland the oxygen barrier may be removed. The lens may be tinted after thecure is completed.

The oxygen barrier may include a flexible, stretchable, self-sealingfilm that is at least partially transparent to ultraviolet rays. Theoxygen barrier may include polyethylene impregnated with aphotoinitiator The film may include a strip of high density polyethylenethat is about 0.01-1.0 mm thick, and more preferably about 0.01-0.10 mmthick. Thicker films tend to be less conformable and stretchable. Theoxygen barrier may include a plastic film that is less than about 0.025mm thick. (e.g., about 0.0127 mm thick) and that was made by (a)immersing or running a plastic film in or through a solution comprisinga photoinitiator and an etching agent (b) removing the plastic film fromthe solution, and (c) drying the plastic film. A surface on the plasticfilm may be chemically etched prior to or while immersing the plasticfilm in the solution.

Another aspect of the invention relates to applying conductive heat tothe face of a lens. In an embodiment of the invention, a liquidpolymerizable lens forming composition is placed in a mold cavity havinga first mold member and a second mold member. First ultraviolet rays maybe directed toward at least one of the mold members to cure the lensforming composition to a lens. A mold member may be applied to asubstantially solid conductive heat source. Heat may be conductivelyapplied to a face of the lens by (a) conductively transferring heat to aface of a mold member from the conductive heat source, and (b)conductively transferring heat through such mold member to the face ofthe lens.

In an embodiment, a flexible heat distributor may be placed between theheat source and the mold member to partially insulate the mold memberand to slowly and uniformly transfer heat to the face of the moldmember. The distributor may be shaped to conform to the face of a moldmember. The heat source may include a concave element that may conformto the convex face of a mold member. The heat source may include aconvex element that may conform to the concave face of a mold member.The temperature of the heat source may be thermostatically controlled.Heat may be conductively applied through a mold member to the back faceof the lens, thereby enhancing the cross-linking and tintability of thelens forming material proximate to the surface of the back face of thelens (e.g., when an untintable scratch resistant coating is on the frontface of the lens).

In an embodiment of the invention an eyeglass lens may be formed by (a)placing a liquid, polymerizable lens-forming composition in a moldcavity defined by at least a first mold member and a second mold member,(b) applying a plurality of preferably high intensity ultraviolet lightpulses to the lens forming composition, at least one of the pulseshaving a duration of less than about one second (more preferably lessthan about 0.1 seconds, and more preferably between 0.1 and 0.001seconds), and (c) curing the lens forming composition to form asubstantially clear eyeglass lens in a time period of less than 30minutes (more preferably less than 20 minutes, and more preferably stillless than 15 minutes).

The pulses preferably have a sufficiently high intensity such thatreaction is initiated in substantially all of the lens formingcomposition that is exposed to pulses in the mold cavity. In oneembodiment reaction is initiated in substantially all of any crosssection of the lens forming composition that is exposed to pulses in themold cavity. Preferably the temperature of the lens forming compositionbegins to rise after such application of UV light.

The lens forming composition may be exposed to UV light from one, two,or multiple sources. Two sources may be applied on opposite sides of themold cavity to apply light to the lens forming composition from twosides. In an alternate embodiment, the lens forming composition isexposed to a relatively low intensity ultraviolet light before or whilethe pulses are applied. Such pulses are preferably relatively high inintensity, and are preferably applied to the other side of the moldcavity than the relatively low intensity light.

The lens forming composition is preferably continuously exposed to arelatively low intensity ultraviolet light either before, while, orafter pulses of relatively high intensity are applied, the relativelylow intensity light having an intensity of less than 1000 microwatts/cm²(and more preferably less than 100 microwatts/cm², and more preferablystill 2-30 microwatts/cm²), as measured on an outside surface of a moldmember of the mold cavity. The relatively low intensity light tends toprovide a low amount of light to keep the reaction going in a moresteady or even manner between pulses.

Preferably at least one or even all of the pulses has an intensity of atleast 0.01 watt/cm², as measured on an outside surface of a mold memberof the mold cavity. Alternately at least one or even all of the pulseshave an intensity of at least 0.1 or 1 watt/cm².

Sufficient ultraviolet light can be applied such that the temperature ofthe lens forming composition begins to increase. Then in one embodimentat least 5 minutes of waiting or darkness occurs before applyingadditional light (e.g., pulses). The waiting or darkness allows heat todissipate, thus tending to prevent excessive heat buildup in the moldcavity. In one embodiment at least 5, 10, or 20 pulses are applied tothe lens forming composition before waiting for about 5-8 minutes andthen additional light is applied.

The eyeglass lens has an average minimum thickness of at least about1.5-2.0 mm. Thicker lenses tend to be more difficult to cure withcontinuous non-pulsed light.

The mold cavity is preferably cooled with air or cooled air. Onesignificant advantage of light pulses is that ambient air may be used tocool the mold cavity, instead of cooled air. Thus significant lenscuring costs may be avoided since air coolers tend to be costly topurchase and operate.

The pulses preferably emanate from a flash source of light (i.e., “aflash light”) such as a xenon light source. Preferably pulses areapplied such that the lens forming composition is oversaturated withultraviolet light during at least one pulse. Flash lights areadvantageous in that they have a short “warm-up” time (as opposed tocontinuous lights that tend to require 5-60 minutes to stabilize).

Lenses may be formed with pulsed light that have more difficult to cureprescriptions such as lenses with a power greater than positive 2diopters, or lenses with a power less than minus 4 diopters.

One advantage of pulsed light application via flash lights is that eventhough higher intensities of light are applied, because the duration ofthe pulses is so short the total amount of light energy applied to curethe lens forming composition is lessened. Thus less radiant heat isapplied to the mold cavity, thereby reducing cooling requirements.Moreover, energy is saved. In one embodiment less than 20, 10, 5, or 1Joule/cm² of energy is applied to cure the lens forming composition intoa lens.

Preferably the ultraviolet light is applied as a function of thetemperature of the lens forming composition, as measured directly orindirectly by measuring a temperature within the chamber (e.g., atemperature of at least a portion of the mold cavity) or by measuring atemperature of air in or exiting the chamber.

In another embodiment of the invention, an eyeglass lens may be cured by(a) placing a liquid, polymerizable lens forming composition in a moldcavity defined by at least a first mold member and a second mold member,the lens forming composition comprising a photoinitiator, (b) applyingultraviolet light at an intensity to the lens forming compositionthrough at least one of the mold members for a selected period of timesuch that a temperature of the composition begins to increase, (c)decreasing the intensity of the ultraviolet light to inhibit thetemperature of the lens forming composition from increasing to aselected first temperature, (d) allowing an exothermic reaction of thelens forming composition to increase the temperature of the lens formingcomposition to a second temperature, the second temperature being lessthan the selected first temperature, (e) curing the lens formingcomposition to form a substantially clear eyeglass lens by: (i) applyingultraviolet light at an intensity to the lens forming compositionthrough at least one of the mold members, and (ii) decreasing theintensity of the ultraviolet light; and (f) wherein the eyeglass lens isformed from the lens forming composition in a time period of less thanabout 30 minutes.

In another embodiment of the invention an eyeglass lens may be made by(a) placing a liquid, polymerizable lens-forming composition in a moldcavity defined by at least a first mold member and a second mold member,the lens forming composition comprising a photoinitiator, (b) applyingfirst ultraviolet light to at least one of the mold members for aselected first period of time such that a temperature of the lensforming composition begins to increase, (c) removing the firstultraviolet light from at least one of the mold members, therebyinhibiting the temperature of the composition from increasing to aselected first temperature, (d) repeatedly and alternately performingthe following steps to complete the formation of a lens: (i) applyingsecond ultraviolet light to at least one of the mold members for aselected second period of time and (ii) removing the second ultravioletlight from at least one of the mold members for a selected third periodof time.

In an alternate embodiment of the invention an eyeglass lens may be madeby (a) placing a liquid, polymerizable lens forming composition in amold cavity defined by at least a first mold member and a second moldmember, the lens forming composition comprising a photoinitiator, (b)directing ultraviolet light at a first intensity toward at least one ofthe mold members for a selected first period of time such that atemperature of the composition begins to increase, (c) decreasing thefirst intensity of ultraviolet light from at least one of the moldmembers, (d) repeatedly directing a plurality of pulses of ultravioletto the lens forming composition through at least one of the mold membersto complete formation of a substantially clear eyeglass lens, at leastone of the pulses lasting for a second period of time, and wherein athird period of time exists between application of at least two of thepulses.

An apparatus of the invention may include: (a) a first mold memberhaving a casting face and a non-casting face, (b) a second mold memberhaving a casting face and a non-casting face, the second mold memberbeing spaced apart from the first mold member during use such that thecasting faces of the first mold member and the second mold member atleast partially define a mold cavity, (c) a first pulse light generatoradapted to generate and direct a pulse of ultraviolet light toward atleast one of the first and second mold members during use, and (d) acontroller adapted to control the first pulse light generator such thatultraviolet light is directed in a plurality of pulses toward at leastone of the first and second mold members, at least one of the pulseshaving a duration of less than one second.

A system of the invention may include (a) a lens forming compositioncomprising a photoinitiator, (b) a first mold member having a castingface and a non-casting face, (c) a second mold member having a castingface and a non-casting face, the second mold member being spaced apartfrom the first mold member during use such that the casting faces of thefirst mold member and the second mold member at least partially define amold cavity for the lens forming composition, (d) a first pulse lightgenerator adapted to generate and direct a pulse of ultraviolet lighttoward at least one of the first and second mold members during use, (e)a controller adapted to control the first pulse light generator suchthat ultraviolet light is directed in a plurality of pulses toward atleast one of the first and second mold members, at least one of thepulses having a duration of less than one second, and (f) wherein thesystem is adapted to cure the lens forming composition to form asubstantially clear eyeglass lens in less than 30 minutes.

The lens forming composition preferably comprises at least onepolyethylenic-functional monomer containing at least two ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, at least onepolyethylenic-functional monomer containing at least three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, and/or anaromatic containing bis(allyl carbonate)-functional monomer.

A system of the invention may include: (a) a lens forming compositioncomprising a photoinitiator, (b) a mold cavity chamber comprising afirst mold member having a casting face and a non-casting face, a secondmold member having a casting face and a non-casting face, the secondmold member being spaced apart from the first mold member during usesuch that the casting faces of the first mold member and the second moldmember at least partially define a mold cavity for the lens formingcomposition, (c) a first light generator adapted to generate and directa ultraviolet light in a first intensity toward at least one of thefirst and second mold members during use, (d) a temperature sensoradapted to sense a temperature in the chamber or a temperature of airexiting the chamber, (e) a controller coupled to the temperature sensorand adapted to control the first light generator such that the firstintensity of ultraviolet light directed toward at least one of the firstand second mold members is decreased when a temperature measured by thetemperature sensor substantially increases, and (f) wherein the systemis adapted to cure the lens forming composition to form a substantiallyclear eyeglass lens in less than 30 minutes.

An apparatus of the invention may include (a) a first mold member havinga casting face and a non-casting face, (b) a second mold member having acasting face and a non-casting face, the second mold member being spacedapart from the first mold member during use such that the casting facesof the first mold member and the second mold member at least partiallydefine a mold cavity for a lens forming composition, (c) an ultravioletlight generator adapted to generate and direct ultraviolet light towardat least one of the first and second mold members during use, (e) acontroller for controlling the intensity of light directed by the lightgenerator, (f) a light sensor adapted, to measure the intensity of lightdirected by the ultraviolet light generator, the light sensor beingadapted to signal the light generator to vary the intensity of theultraviolet light being produced, and (g) a filter adapted to inhibitlight other than ultraviolet light from impinging upon the light sensor.

In an alternate embodiment, a system for making an eyeglass lens mayinclude (a) a first mold member having a casting face and a non-castingface, (b) a second mold member having a casting face and a non-castingface, the second mold member being spaced apart from the first moldmember during use such that the casting faces of the first mold memberand the second mold member at least partially define a mold cavity for alens forming composition, (c) an ultraviolet light generator adapted togenerate and direct ultraviolet light toward at least one of the firstand second mold members during use, (d) a distributor adapted to directair toward the non-casting face of at least one of the mold members, (e)a thermoelectric cooling system adapted to cool the air, and (f) a firstblower adapted to receive effluent air that has contacted thenon-casting face of the mold member and to recycle the effluent air tothe distributor.

In an embodiment, an eyeglass lens may be made by (a) placing a liquid,polymerizable lens forming composition in a mold cavity defined at leastpartially by a first mold member and a second mold member, the lensforming composition comprising a photoinitiator; (b) directing aplurality of pulses of ultraviolet light toward the lens formingcomposition through at least one of the mold members to initiatereaction of the lens forming composition, at least one of the pulseshaving an intensity of at least about 10 milliwatts/cm²; (c) subsequentto the step of directing the plurality of pulses toward the lens formingcomposition, directing ultraviolet light of a second intensity towardthe lens forming composition through at least one of the mold members toform a substantially clear eyeglass lens, the second intensity beingless than about 350 microwatts/cm²; and (d) substantially simultaneouslywith the step of directing ultraviolet of a second intensity toward thelens forming composition, directing air onto a non-casting face of atleast one of the mold members to remove heat from the lens formingcomposition.

A lens having a scratch resistant coating may be formed by: placing afirst coating composition within a mold member, the mold membercomprising a casting face and a non-casting face, the coatingcomposition comprising a photoinitiator and being curable upon exposureto ultraviolet light; (a) placing a first coating composition within amold member, the mold member comprising a casting face and a non-castingface, the coating composition comprising a photoinitiator and beingcurable upon exposure to ultraviolet light; (b) spinning the mold memberto distribute the first coating composition over the casting face; (c)directing ultraviolet light at the mold member to cure at least aportion of the first coating composition; (d) placing a second coatingcomposition within the mold member, the second coating compositioncomprising a photoinitiator and being curable upon exposure toultraviolet light; (e) spinning the mold member to distribute the secondcoating composition over the portion of the first coating compositionthat has been cured; (f) directing ultraviolet light at the mold member,thereby curing at least a portion of the second coating composition andforming a substantially clear combination coat comprising at least aportion of each of the first and second coating compositions; (g)assembling the mold member with a second mold member to form a moldhaving a cavity between the mold members; (h) placing a lens-formingcomposition within the cavity, the lens-forming composition comprising aphotoinitiator and being curable upon exposure to ultraviolet light; and(i) directing ultraviolet light at the mold to cure at least a portionof the lens-forming material to form a lens, and wherein the combinationcoat adheres to the cured portion of the lens-forming material.

In an embodiment, a lens forming composition containing the followingcomponents may be used to cure an eyeglass lens that does not transmitultraviolet light. The composition preferably comprises (a) a monomercapable of being cured to form an eyeglass lens, (b) an ultravioletabsorbing compound for inhibiting at least a portion of ultravioletlight from being transmitted through the eyeglass lens, (c) aco-initiator adapted to activate curing of the monomer to form theeyeglass lens, and (d) a photoinitiator adapted to activate theco-initiator in response to being exposed to ultraviolet light.

In another embodiment, a lens forming composition containing thefollowing components may be used to cure an eyeglass lens that does nottransmit ultraviolet light. The composition preferably comprises (a) amonomer capable of being cured to form an eyeglass lens, (b) anultraviolet absorbing compound for inhibiting at least a portion ofultraviolet light from being transmitted through the eyeglass lens, and(c) a photoinitiator adapted to activate curing of the monomer to formthe eyeglass lens. The monomer may be cured by treatment with activatinglight. The activating light preferably includes light having awavelength substantially greater than about 380 nm.

In an embodiment, the conditions whereby a lens is formed from a lensforming composition may be altered such that the formed lens has a powersubstantially different from the targeted power of the lens. The peaktemperature of the composition may be preferably altered such thatlenses formed at elevated peak temperatures may have a lens power lowerthan targeted from the shape of the mold cavity. Alternatively, the timeat which the lenses are removed from the lens forming mold may bealtered such that lenses that are released at an earlier time from themold may have a power substantially greater than targeted from the shapeof the mold cavity.

In an embodiment, the lens forming process may be controlled using amicroprocessor based controller. The controller preferably monitors theresponse of the lens forming composition to a pulse of activating light.The controller preferably measures the temperature and the rate oftemperature change during the process. While the lens is no longer beingirradiated with activating light, the controller preferably monitors thetemperature curves and performs a mathematical analysis of thetemperature curve profile. Dosages of activating light, based on theresponse of the composition to the last activating light applied, may bedetermined and applied. This process may be repeated until the lens issubstantially cured.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description as well as further objects, features andadvantages of the methods and apparatus of the present invention will bemore fully appreciated by reference to the following detaileddescription of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an apparatus for producing a plasticlens.

FIG. 2 is a cross-sectional view of the apparatus taken along line 2—2of FIG. 1.

FIG. 3 is a cross-sectional view of the apparatus taken along line 3—3of FIG. 2.

FIG. 4 is a detail view of a component of the apparatus.

FIG. 5 is a detail view of a component of the apparatus.

FIG. 6 is a cross-sectional view of a lens cell for use in an apparatusof the invention.

FIG. 7 is a view of an embodiment of a shutter system.

FIG. 8 is a top and side view of an embodiment of a heat distributor tobe placed between a heat source and a mold surface.

FIG. 9 is a schematic block diagram of an alternate process and systemfor making and postcuring a plastic lens.

FIG. 10 is a schematic diagram of an apparatus to apply UV light to alens or mold assembly.

FIG. 11 is a view of an embodiment of a lens.

FIG. 12 is a view of an embodiment of an oxygen barrier withphotoinitiator.

FIG. 13 is a schematic diagram of a lens curing apparatus with a lightsensor and controller.

FIG. 14 is a schematic view of the front of a lens curing apparatus.

FIG. 15 is a schematic view of the side of a lens curing apparatus.

FIG. 16 is a view of an embodiment of a heat source and a heatdistributor.

FIG. 17 is a view of various embodiments of a heat source and heatdistributors.

FIG. 18 is a view of an embodiment of a heat source and a heatdistributor.

FIG. 19 is a view of an embodiment of two mold members and a gasket.

FIG. 20 is a graph illustrating a temperature profile of a continuousradiation cycle.

FIG. 21 is a graph illustrating temperature profiles for a continuousirradiation cycle and a pulse irradiation cycle employed with amold/gasket set having a 3.00 D base curve, and while applying cooledair at 58° F. to the mold/gasket set.

FIG. 22 is a chart illustrating qualitative relationships among curingcycle variables.

FIG. 23 is a graph illustrating temperature profiles for one curingcycle for a mold/gasket set having a 6.00 D base curve and used withthree different light levels.

FIG. 24 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 6.00 Dbase curve.

FIG. 25 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 4.50 Dbase curve.

FIG. 26 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 3.00 Dbase curve.

FIG. 27 is a view of an embodiment of a system simultaneously employingboth a flash light source and a continuous UV (e.g., fluorescent)source.

FIG. 28 is an embodiment of a system simultaneously employing two flashlight sources.

FIG. 29 is an embodiment of a system employing an ultraviolet lightcontroller.

FIG. 30 depicts a schematic view of a lens curing apparatus.

FIG. 31 depicts a detail view of a thermoelectric cooling system.

FIG. 32 depicts a cross sectional view of a thermoelectric coolingsystem.

FIG. 33 depicts a thermoelectric module.

FIG. 34 depicts a flash lamp curing cycle.

FIG. 35 depicts a cross sectional view of a flat-top bifocal mold.

FIG. 36 depicts a cross sectional view of a filter disposed directlyadjacent to a mold member.

FIG. 37 depicts a plot of % transmittance of light versus wavelength fora photochromic lens.

FIG. 38 depicts a plot of % transmittance of light versus wavelength forboth a colorless lens containing ultraviolet absorbers and a lenscontaining no ultraviolet absorbers.

FIG. 39 depicts a plot of % transmittance of light versus wavelength fora colored lens containing fixed pigments.

FIG. 40 depicts a plot of the temperature of the lens formingcomposition versus time during the application of activating lightpulses.

DESCRIPTION OF A PREFERRED EMBODIMENTS

Apparatus, operating procedures, equipment, systems, methods, andcompositions for lens curing using ultraviolet light are available fromRapid Cast, Inc., Q2100, Inc., and Fast Cast, Inc. in East Rockaway,N.Y. and Louisville, Ky. The Fast Cast, Inc. publication entitled“Operation Manual For The FastCast LenSystem” is hereby incorporated byreference.

Referring now to FIG. 1, a plastic lens curing chamber of the presentinvention is generally indicated by reference numeral 10. The lenscuring chamber 10 preferably communicates through a plurality of pipes12 with an air source (not shown), the purpose of which will bediscussed below.

As shown in FIG. 2, the plastic lens curing chamber 10 may include anupper lamp chamber 14, an irradiation chamber 16, and a lower lampchamber 18. The upper lamp chamber 14 may be separated from theirradiation chamber 16 by a plate 20. The lower lamp chamber may beseparated from the irradiation chamber 16 by a plate 22. The upper lampchamber 14, the irradiation chamber 16, and the lower lamp chamber 18may be isolated from ambient air by upper lamp chamber doors 24,irradiation chamber doors 26, and lower lamp chamber doors 28,respectively. While the upper lamp chamber doors 24, the irradiationchamber doors 26 and the lower lamp chamber doors 28 are shown in FIG. 1as including two corresponding door members, those of ordinary skill inthe art will recognize that the doors 24, 26 and 28 may include singleor multiple door members. The upper lamp chamber doors 24, theirradiation chamber doors 26 and the lower lamp chamber doors 28 may beslidingly mounted in guides 30. As shown in FIG. 2, vents 32 maycommunicate with upper lamp chamber 14 and lower lamp chamber 18 by wayof corresponding vent chambers 34 and openings 36 disposed in plate 20and plate 22. Each vent 32 may be shielded by a vent cover 38.

As shown in FIG. 3, vents 33 may be disposed in the irradiation chamberdoors 26 and communicate with irradiation chamber 16. Each vent 33 maybe shielded by a vent cover 35.

As shown in FIGS. 2 and 3, a plurality of light generating devices orlamps 40 may be disposed within each of upper lamp chamber 14 and lowerlamp chamber 18. Preferably, upper lamp chamber 14 and lower lampchamber 18 each include three lamps 40 that are arranged in a triangularfashion in which the lamps 40 in the upper lamp chamber 14 are disposedwith the point of the triangle pointing upwards whereas the lamps 40 inthe lower lamp chamber 18 are disposed with the point of the trianglepointing downward. The lamps 40, preferably, generate ultraviolet lighthaving a wavelength in the range of at least approximately 300 nm to 400nm since the effective wavelength spectrum for curing the lens formingmaterial lies in the 300 nm to 400 nm region. The lamps 40 may besupported by and electrically connected to suitable fixtures 42.

An exhaust fan 44 may communicate with upper lamp chamber 14 while anexhaust fan 46 may communicate with lower lamp chamber 18.

As noted above, the upper lamp chamber 14 may be separated from theirradiation chamber 16 by plate 20. Similarly, lower lamp chamber 18 maybe separated from the irradiation chamber 16 by plate 22. The plates 20and 22 may include apertures 48 and 50, respectively, through which thelight generated by lamps 40 may be directed so as to impinge upon a lenscell 52 (shown in phantom in FIG. 2). The diameter of the lens cell 52is preferably approximately 74 mm. The apertures 48 and 50 preferablyrange from about 70 mm to about 140 mm.

In one embodiment an upper light filter 54 rests upon plate 20 while alower light filter 56 rests upon plate 22 or is supported by brackets57. The upper light filter 54 and lower light filter 56 are shown inFIG. 2 as being made of a single filter member, however, those ofordinary skill in the art will recognize that each of the upper lightfilter 54 and lower light filter 56 may include two or more filtermembers. The components of upper light filter 54 and lower light filter56 preferably are modified depending upon the characteristics of thelens to be molded. For instance, in a preferred embodiment for makingnegative lenses, the upper light filter 54 includes a plate of Pyrexglass that is frosted on both sides resting upon a plate of clear Pyrexglass. The lower light filter 56 includes a plate of Pyrex glass frostedon one side resting upon a plate of clear Pyrex glass with a device forreducing the intensity of ultraviolet light incident upon the centerportion in relation to the edge portion of the lens being disposedbetween the plate of frosted Pyrex and the plate of clear Pyrex glass.

Conversely, in a preferred arrangement for producing positive lenses,the upper light filter 54 includes a plate of Pyrex glass frosted on oneor both sides and a plate of clear Pyrex glass resting upon the plate offrosted Pyrex glass with a device for reducing the intensity ofultraviolet light incident upon the edge portion in relation to thecenter portion of the lens being disposed between the plate of clearPyrex glass and the plate of frosted Pyrex glass. The lower light filter56 includes a plate of clear Pyrex glass frosted on one side restingupon a plate of clear Pyrex glass with a device for reducing theintensity of ultraviolet light incident upon the edge portion inrelation to the center portion of the lens being disposed between theplates of clear Pyrex glass. In this arrangement, in place of a devicefor reducing the relative intensity of ultraviolet light incident uponthe edge portion of the lens, the diameter of the aperture 50 can bereduced to achieve the same result, i.e. to reduce the relativeintensity of ultraviolet light incident upon the edge portion of thelens.

It will be apparent to those skilled in the art that each filter 54 or56 could be composed of a plurality of filter members or include anyother means or device effective to reduce the light to its desiredintensity, to diffuse the light and/or to create a light intensitygradient across the lens cell 52. Alternately, in certain embodiments nofilter elements may be used.

Preferably, the upper light filter 54 or the lower light filter 56 eachinclude at least one plate of Pyrex glass having at least one frostedsurface. Also, either or both of the upper light filter 54 and the lowerlight filter 56 may include more than one plate of Pyrex glass eachfrosted on one or both surfaces, and/or one or more sheets of tracingpaper. After passing through frosted Pyrex glass, the ultraviolet lightis believed to have no sharp intensity discontinuities which is believedto lead to a reduction in optical distortions in the finished lens insome instances. Those of ordinary skill in the art will recognize thatother means may be used to diffuse the ultraviolet light so that it hasno sharp intensity discontinuities.

Preferably disposed within the irradiation chamber 16 are a left stage58, a center stage 60, and a right stage 62, each of which preferablyincludes a plurality of steps 64. The left stage 58 and center stage 60define a left irradiation chamber 66 while the right stage 62 and centerstage 60 define a right irradiation chamber 68. A cell holder 70, shownin phantom in FIG. 2 and in detail in FIG. 4, may be disposed withineach of left irradiation chamber 66 and right irradiation chamber 68.The cell holder 70 may include a peripheral step 72 that is designed toallow a cell holder 70 to be supported upon complementary steps 64 ofleft stage 58 and center stage 60, and center stage 60 and right stage62, respectively. As shown in FIG. 4, each cell holder 70 also mayinclude a central bore 74 to allow the passage therethrough ofultraviolet light from the lamps 40 and an annular step 76 which isdesigned to support a lens cell 52 in a manner described below.

As shown in FIG. 6, each lens cell 52 may include opposed mold members78, separated by an annular gasket 80 to define a lens molding cavity82. The opposed mold members 78 and the annular gasket 80 may be shapedand selected in a manner to produce a lens having a desired diopter.

The mold members 78 are preferably formed of any suitable material thatwill permit rays of ultraviolet light to pass therethrough. The moldmembers 78 are preferably formed of glass. Each mold member 78 has anouter peripheral surface 84 and a pair of opposed surfaces 86 and 88with the surfaces 86 and 88 being precision ground. Preferably the moldmembers 78 have desirable ultraviolet light transmission characteristicsand both the casting surface 86 and non-casting surface 88 preferablyhave no surface aberrations, waves, scratches or other defects as thesemay be reproduced in the finished lens.

As noted above, the mold members 78 are adapted to be held in spacedapart relation to define a lens molding cavity 82 between the facingsurfaces 86 thereof. The mold members 78 are preferably held in a spacedapart relation by a T-shaped flexible annular gasket 80 that seals thelens molding cavity 82 from the exterior of the mold members 78. In use,the gasket 80 may be supported on the annular step 76 of the cell holder70.

In this manner, the upper or back mold member 90 has a convex innersurface 86 while the lower or front mold member 92 has a concave innersurface 86 so that the resulting lens molding cavity 82 is shaped toform a lens with a desired configuration. Thus, by selecting the moldmembers 78 with a desired surface 86, lenses with differentcharacteristics, such as focal lengths, may be made by the apparatus 10.

Rays of ultraviolet light emanating from lamps 40 pass through the moldmembers 78 and act on a lens forming material disposed in the moldcavity 82 in a manner discussed below so as to form a lens. As notedabove, the rays of ultraviolet light may pass through a suitable filter54 or 56 to impinge upon the lens cell 52.

The mold members 78, preferably, are formed from a material that willnot allow ultraviolet radiation having a wavelength below approximately300 nm to pass therethrough. Suitable materials are Schott Crown, S-1 orS-3 glass manufactured and sold by Schott Optical Glass Inc., of Duryea,Pa. or Corning 8092 glass sold by Corning Glass of Corning, N.Y. Asource of flat-top or single vision molds may be Augen Lens Co. in SanDiego, Calif.

The annular gasket 80 may be formed of vinyl material that exhibits goodlip finish and maintains sufficient flexibility at conditions throughoutthe lens curing process. In a preferred embodiment, the annular gasket80 is formed of silicone rubber material such as GE SE6035 which iscommercially available from General Electric. In another preferredembodiment, the annular gasket 80 is formed of copolymers of ethyleneand vinyl acetate which are commercially available from E. I. DuPont deNemours & Co. under the trade name ELVAX7. Preferred ELVAX7 resins areELVAX7 350 having a melt index of 17.3-20.9 dg/min and a vinyl acetatecontent of 24.3-25.7 wt. %, ELVAX7 250 having a melt index of 22.0-28.0dg/min and a vinyl acetate content of 27.2-28.8 wt. %, ELVAX7 240 havinga melt index of 38.0-48.0 dg/min and a vinyl acetate content of27.2-28.8 wt. %, and ELVAX7 150 having a melt index of 38.0-48.0 dg/minand a vinyl acetate content of 32.0-34.0 wt. %. Regardless of theparticular material, the gaskets 80 may be prepared by conventionalinjection molding or compression molding techniques which are well-knownby those of ordinary skill in the art.

As shown in phantom in FIG. 2, in section in FIG. 3, and in detail inFIG. 5, an upper and lower air distribution device 94 is disposed ineach of left irradiation chamber 66 and right irradiation chamber 68.Each air distribution device 94 is connected to a pipe 12. As shown inFIG. 5, each air distribution device 94 includes a plenum portion 95 anda substantially cylindrical opening 96 having orifices 98 disposedtherein to allow for the expulsion of air from the air distributiondevice 94. The diameter of the orifices 98 may be constant, or may varyaround the circumference of cylindrical opening 96 preferably reaching amaximum when directly opposite the plenum portion 95 of air distributiondevice 94 and preferably reaching a minimum immediately adjacent theplenum portion 95. In addition, the orifices 98 are designed to blow airtoward a lens cell 52 that may be disposed in a lens cell holder 70 andinstalled in left irradiation chamber 66 or right irradiation chamber68.

In operation, the apparatus of the present invention may beappropriately configured for the production of positive lenses which arerelatively thick at the center or negative lenses which are relativelythick at the edge. To reduce the likelihood of premature release, therelatively thick portions of a lens preferably are polymerized at afaster rate than the relatively thin portions of a lens.

The rate of polymerization taking place at various portions of a lensmay be controlled by varying the relative intensity of ultraviolet lightincident upon particular portions of a lens. The rate of polymerizationtaking place at various portions of a lens may also be controlled bydirecting air across the mold members 78 to cool the lens cell 52.

For positive lenses the intensity of incident ultraviolet light ispreferably reduced at the edge portion of the lens so that the thickercenter portion of the lens polymerizes faster than the thinner edgeportion of the lens. Conversely, for a negative lens, the intensity ofincident ultraviolet light is preferably reduced at the center portionof the lens so that the thicker edge portion of the lens polymerizesfaster than the thinner center portion of the lens. For either apositive lens or a negative lens, air may be directed across the facesof the mold members 78 to cool the lens cell 52. As the overallintensity of incident ultraviolet light is increased, more cooling isneeded which can be accomplished by either or both of increasing thevelocity of the air and reducing the temperature of the air.

It is well known by those of ordinary skill in the art that lens formingmaterials having utility in the present invention tend to shrink as theycure. If the relatively thin portion of a lens is allowed to polymerizebefore the relatively thick portion, the relatively thin portion willtend to be rigid at the time the relatively thick portion cures andshrinks and the lens will either release prematurely from or crack themold members 78. Accordingly, when the relative intensity of ultravioletlight incident upon the edge portion of a positive lens is reducedrelative to the center portion, the center portion polymerizes fasterand shrinks before the edge portion is rigid so that the shrinkage ismore uniform. Conversely, when the relative intensity of ultravioletlight incident upon the center portion of a negative lens is reducedrelative to the edge portion, the edge portion polymerizes faster andshrinks before the center becomes rigid so that the shrinkage is moreuniform.

The variation of the relative intensity of ultraviolet light incidentupon a lens may be accomplished in a variety of ways. According to onemethod, in the case of a positive lens, a ring of opaque material may beplaced between the lamps 40 and the lens cell 52 so that the incidentultraviolet light falls mainly on the thicker center portion of thelens. Conversely, for a negative lens, a disk of opaque material may beplaced between the lamps 40 and the lens cell 52 so that the incidentultraviolet light falls mainly on the edge portion of the lens.

According to another method, in the case of a negative lens, a sheetmaterial having a variable degree of opacity ranging from opaque at acentral portion to transparent at a radial outer portion is disposedbetween the lamps 40 and the lens cell 52. Conversely, for a positivelens, a sheet material having a variable degree of opacity ranging fromtransparent at a central portion to opaque at a radial outer portion isdisposed between the lamps 40 and the lens cell 52.

Those of ordinary skill in the art will recognize that there are a widevariety of techniques other than those enumerated above for varying theintensity of the ultraviolet light incident upon the opposed moldmembers 78.

In some embodiments, the intensity of the incident light has beenmeasured and determined to be approximately 3.0 to 5.0 milliwatts persquare centimeter (mW/cm²) prior to passing through either the upperlight filter 54 or the lower light filter 56 and the total intensity atthe thickest part of the lens ranges from 0.6 to 2.0 mW/cm² while theintensity at the thinnest portion of the lens ranges from 0.1 to 1.5mW/cm². In some embodiments the overall light intensity incident on thelens cell 52 has less of an impact on the final product than therelative light intensity incident upon the thick or thin portions of thelens so long as the lens cell 52 is sufficiently cooled to reduce thepolymerization rate to an acceptable level.

In addition, as described below, in certain embodiments heat may beconductively applied to the molds and/or lens, thereby enhancing thequality of the cured lenses.

The ultraviolet lamps 40 preferably are maintained at a temperature atwhich the lamps 40 deliver maximum output. The lamps 40, preferably, arecooled because the intensity of the light produced by the lamps 40fluctuates when the lamps 40 are allowed to overheat. In the apparatusdepicted in FIG. 2, the cooling of the lamps 40 is accomplished bysucking ambient air into the upper lamp chamber 14 and lower lampchamber 18 through vent 32, vent chambers 34 and openings 36 by means ofexhaust fans 44 and 46, respectively. Excessive cooling of the lamps 40should be avoided, however, as the intensity of the light produced bythe lamps 40 is reduced when the lamps 40 are cooled to an excessivedegree.

As noted above, the lens cell 52 is preferably cooled during curing ofthe lens forming material as the overall intensity of the incidentultraviolet light is increased. Cooling of the lens cell 52 generallyreduces the likelihood of premature release by slowing the reaction andimproving adhesion. There are also improvements in the optical quality,stress characteristics and impact resistance of the lens. Cooling of thelens cell 52 is preferably accomplished by blowing air across the lenscell 52. The air preferably has a temperature ranging between 15 and 85°F. (about −9.4° C. to 29.4° C.) to allow for a curing time of between 30and 10 minutes. The air distribution devices 94 depicted in FIG. 5 havebeen found to be particularly advantageous as they are specificallydesigned to direct air directly across the surface of the opposed moldmembers 78. After passing across the surface of the opposed mold members78, the air emanating from the air distribution devices 94 is ventedthrough vents 33. Alternately the air emanating from the airdistribution devices 94 may be recycled back to an air cooler.

The lens cell 52 may also be cooled by disposing the lens cell in aliquid cooling bath.

The opposed mold members 78 are preferably thoroughly cleaned betweeneach curing run as any dirt or other impurity on the mold members 78 maycause premature release. The mold members 78 are cleaned by anyconventional means well known to those of ordinary skill in the art suchas with a domestic cleaning product, i e., Mr. Clean™ available fromProctor and Gamble. Those of ordinary skill in the art will recognize,however, that many other techniques may also be used for cleaning themold members 78.

Yellowing of the finished lens may be related to the monomercomposition, the identity of the photoinitiator, and the concentrationof the photoinitiator.

When casting a lens, particularly a positive lens that is thick in thecenter, cracking may be a problem. Addition polymerization reactions,including photochemical addition polymerization reactions, areexothermic. During the process, a large temperature gradient may buildup and the resulting stress may cause the lens to crack.

The formation of optical distortions usually occurs during the earlystages of the polymerization reaction during the transformation of thelens forming composition from the liquid to the gel state. Once patternsleading to optical distortions form they are difficult to eliminate.When gelation occurs there typically is a rapid temperature rise. Theexothermic polymerization step causes a temperature increase, which inturn causes an increase in the rate of polymerization, which causes afurther increase in temperature. If the heat exchange with thesurroundings is not sufficient enough there will be a runaway situationthat leads to premature release, the appearance of thermally causedstriations and even breakage.

Accordingly, when continuous UV light is applied, it is preferred thatthe reaction process be smooth and not too fast but not too slow. Heatis preferably not generated by the process so fast that it cannot beexchanged with the surroundings. The incident ultraviolet lightintensity preferably is adjusted to allow the reaction to proceed at adesired rate. It is also preferred that the seal between the annulargasket 80 and the opposed mold members 78 be as complete as possible.

Factors that have been found to lead to the production of lenses thatare free from optical distortions are (1) achieving a good seal betweenthe annular gasket 80 and the opposed mold members 78; (2) using moldmembers 78 having surfaces that are free from defects; (3) using aformulation having an appropriate type and concentration ofphotoinitiator that will produce a reasonable rate of temperature rise;and (4) using a homogeneous formulation. Preferably, these conditionsare optimized.

Premature release of the lens from the mold will result in anincompletely cured lens and the production of lens defects. Factors thatcontribute to premature release are (1) a poorly assembled lens cell 52;(2) the presence of air bubbles around the sample edges; (3)imperfection in gasket lip or mold edge; (4) inappropriate formulation;(5) uncontrolled temperature rise; and (6) high or nonuniform shrinkage.Preferably, these conditions are minimized.

Premature release may also occur when the opposed mold members 78 areheld too rigidly by the annular gasket 80. Preferably, there issufficient flexibility in the annular gasket 80 to permit the opposedmold members 78 to follow the lens as it shrinks. Indeed, the lens mustbe allowed to shrink in diameter slightly as well as in thickness. Theuse of an annular gasket 80 that has a reduced degree of stickiness withthe lens during and after curing is therefore desirable.

In a preferred technique for filling the lens molding cavity 82, theannular gasket 80 is placed on a concave or front mold member 92 and aconvex or back mold member 90 is moved into place. The annular gasket 80is then pulled away from the edge of the back mold member 90 at theuppermost point and a lens forming composition is injected into the lensmolding cavity 82 until a small amount of the lens forming compositionis forced out around the edge. The excess is then removed, preferably,by vacuum. Excess liquid that is not removed could spill over the faceof the back mold member 90 and cause optical distortion in the finishedlens.

Despite the above problems, the advantages offered by the radiationcured lens molding system clearly outweigh the disadvantages. Theadvantages of a radiation cured system include a significant reductionin energy requirements, curing time and other problems normallyassociated with conventional thermal systems.

The lens forming material may include any suitable liquid monomer ormonomer mixture and any suitable photosensitive initiator. As usedherein “monomer” is taken to mean any compound capable of undergoing apolymerization reaction. Monomers may include non-polymerized materialor partially polymerized material. When partially polymerized materialis used as a monomer, the partially polymerized material preferablycontains functional groups capable of undergoing further reaction toform a new polymer. The lens forming material, preferably, does notinclude any component, other than a photoinitiator, that absorbsultraviolet light having a wavelength in the range of 300 to 400 nm. Theliquid lens forming material is preferably filtered for quality controland placed in the lens molding cavity 82 by pulling the annular gasket80 away from one of the opposed mold members 78 and injecting the liquidlens forming material into the lens molding cavity 82. Once the lensmolding cavity 82 is filled with such material, the annular gasket 80 isreplaced into its sealing relation with the opposed mold members 78.

Those skilled in the art will recognize that once the cured lens isremoved from the lens molding cavity 82 by disassembling the opposedmold members 78, the lens can be further processed in a conventionalmanner, such as by grinding its peripheral edge.

According to the present invention a polymerizable lens formingcomposition includes an aromatic-containing bis(allylcarbonate)-functional monomer and at least one polyethylenic-functionalmonomer containing two ethylenically unsaturated groups selected fromacrylyl and methacrylyl. In a preferred embodiment, the compositionfurther includes a suitable photoinitiator. In other preferredembodiments, the composition may include one or morepolyethylenic-functional monomers containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, and a dye.

Aromatic-containing bis(allyl carbonate)-functional monomers which canbe utilized in the practice of the present invention are bis(allylcarbonates) of dihydroxy aromatic-containing material. The dihydroxyaromatic-containing material from which the monomer is derived may beone or more dihydroxy aromatic-containing compounds. Preferably thehydroxyl groups are attached directly to nuclear aromatic carbon atomsof the dihydroxy aromatic-containing compounds. The monomers arethemselves known and can be prepared by procedures well known in theart.

The aromatic-containing bis(allyl carbonate)-functional monomers can berepresented by the formula:

in which A₁ is the divalent radical derived from the dihydroxyaromatic-containing material and each R₀ is independently hydrogen,halo, or a C₁-C₄ alkyl group. The alkyl group is usually methyl orethyl. Examples of R₀ include hydrogen, chloro, bromo, fluoro, methyl,ethyl, n-propyl, isopropyl and n-butyl. Most commonly R₀ is hydrogen ormethyl; hydrogen is preferred. A subclass of the divalent radical A₁which is of particular usefulness is represented by the formula:

in which each R₁ is independently alkyl containing from 1 to about 4carbon atoms, phenyl, or halo; the average value of each a isindependently in the range of from 0 to 4; each Q is independently oxy,sulfonyl, alkanediyl having from 2 to about 4 carbon atoms, oralkylidene having from 1 to about 4 carbon atoms; and the average valueof n is in the range of from 0 to about 3. Preferably Q ismethylethylidene, viz., isopropylidene.

Preferably the value of n is zero, in which case A₁ is represented bythe formula:

in which each R₁, each a, and Q are as discussed in respect of FormulaII. Preferably the two free bonds are both in the ortho or parapositions. The para positions are especially preferred.

The dihydroxy aromatic-containing compounds from which A₁ is derived mayalso be polyol-functional chain extended compounds. Examples of suchcompounds include alkaline oxide extended bisphenols. Typically thealkaline oxide employed is ethylene oxide, propylene oxide, or mixturesthereof. By way of exemplification, when para, para-bisphenols are chainextended with ethylene oxide, the bivalent radical A₁ may often berepresented by the formula:

where each R₁, each a, and Q are as discussed in respect of Formula II,and the average values of j and k are each independently in the range offrom about 1 to about 4.

A preferred aromatic-containing bis(allyl carbonate)-functional monomeris represented by the formula:

and is commonly known as bisphenol A bis(allyl carbonate).

A wide variety of compounds may be used as the polyethylenic functionalmonomer containing two or three ethylenically unsaturated groups. Apreferred polyethylenic functional compounds containing two or threeethylenically unsaturated groups may be generally described as theacrylic acid esters and the methacrylic acid esters of aliphaticpolyhydric alcohols, such as, for example, the di- and triacrylates andthe di- and trimethacrylates of ethylene glycol, triethylene glycol,tetraethylene glycol, tetramethylene glycol, glycidol, diethyleneglycol,butyleneglycol, propyleneglycol, pentanediol, hexanediol,trimethylolpropane, and tripropyleneglycol. Examples of specificsuitable polyethylenic—functional monomers containing two or threeethylenically unsaturated groups include trimethylolpropanetriacrylate(TMPTA), tetraethylene glycol diacrylate (TTEGDA), tripropylene glycoldiacrylate (TRPGDA), 1,6 hexanedioldimethacrylate (HDDMA), andhexanedioldiacrylate (HDDA).

In general, a photoinitiator for initiating the polymerization of thelens forming composition of the present invention, preferably, exhibitsan ultraviolet absorption spectrum over the 300-400 nm range. Highabsorptivity of a photoinitiator in this range, however, is notdesirable, especially when casting a thick lens. The following areexamples of illustrative photoinitiator compounds within the scope ofthe invention: methyl benzoylformate,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenylketone, 2,2-di-sec-butoxyacetophenone, 2,2-diethoxyacetophenone,2,2-diethoxy-2-phenyl-acetophenone, 2,2-dimethoxy-2-phenyl-acetophenone,benzoin methyl ether, benzoin isobutyl ether, benzoin, benzil, benzyldisulfide, 2,4-dihydroxybenzophenone, benzylideneacetophenone,benzophenone and acetophenone. Preferred photoinitiator compounds are1-hydroxycyclohexyl phenyl ketone (which is commercially available fromCiba-Geigy as Irgacure 184), methyl benzoylformate (which iscommercially available from Polysciences, Inc.), or mixtures thereof.

Methyl benzoylformate is a generally preferred photoinitiator because ittends to provide a slower rate of polymerization. The slower rate ofpolymerization tends to prevent excessive heat buildup (and resultantcracking of the lens) during polymerization. In addition, it isrelatively easy to mix liquid methyl benzoylformate (which is liquid atambient temperatures) with many acrylates, diacrylates, and allylcarbonate compounds to form a lens forming composition. The lensesproduced with the methyl benzoylformate photoinitiator tend to exhibitmore favorable stress patterns and uniformity.

A strongly absorbing photoinitiator will absorb most of the incidentlight in the first millimeter of lens thickness, causing rapidpolymerization in that region. The remaining light will produce a muchlower rate of polymerization below this depth and will result in a lensthat has visible distortions. An ideal photoinitiator will exhibit highactivity, but will have a lower extinction coefficient in the usefulrange. A lower extinction coefficient of photoinitiators at longerwavelengths tends to allow the ultraviolet radiation to penetrate deeperinto the reaction system. This deeper penetration of the ultravioletradiation allows photoinitiator radicals to form uniformly throughoutthe sample and provide excellent overall cure. Since the sample can beirradiated from both top and bottom, a system in which appreciable lightreaches the center of the thickest portion of the lens is preferred. Thephotoinitiator solubility and compatibility with the monomer system isalso an important requirement.

An additional consideration is the effect of the photoinitiatorfragments in the finished polymer. Some photoinitiators generatefragments that impart a yellow color to the finished lens. Although suchlenses actually absorb very little visible light, they are cosmeticallyundesirable.

Photoinitiators are often very system specific so that photoinitiatorsthat are efficient in one system may function poorly in another. Inaddition, the initiator concentration to a large extent is dependent onthe incident light intensity and the monomer composition. The identityof the initiator and its concentration are important for any particularformulation. A concentration of initiator that is too high tends to leadto cracking and yellowing of the lens. Concentrations of initiator thatare too low tend to lead to incomplete polymerization and a softmaterial.

Dyes and/or pigments are optional materials that may be present whenhigh transmission of light is not necessary.

The listing of optional ingredients discussed above is by no meansexhaustive. These and other ingredients may be employed in theircustomary amounts for their customary purposes so long as they do notseriously interfere with good polymer formulating practice.

According to a preferred embodiment of the present invention, apreferred aromatic-containing bis(allyl carbonate) functional monomer,bisphenol A bis(allyl carbonate) is admixed with one or more fasterreacting polyethylenic functional monomers containing two acrylate ormethacrylate groups such as 1,6 hexanediol dimethacrylate (HDDMA), 1,6hexanediol diacrylate (HDDA), tetraethylene glycol diacrylate (TTEGDA),and tripropylene glycol diacrylate (TRPGDA) and optionally apolyethylenic functional monomer containing three acrylate groups suchas trimethylolpropane triacrylate (TMPTA). Generally, compoundscontaining acrylate groups polymerize much faster than those containingallyl groups.

In one embodiment, the lamps 40 generate an intensity at the lampsurface of approximately 4.0 to 7.0 mW/cm² of ultraviolet light havingwavelengths between 300 and 400 nm, which light is very uniformlydistributed without any sharp discontinuities throughout the reactionprocess. Such bulbs are commercially available from Sylvania under thetrade designation Sylvania Fluorescent (F15T8/2052) or SylvaniaFluorescent (F15T8/350BL/18″) GTE.

As noted above, ultraviolet light having wavelengths between 300 and 400nm is preferred because the photoinitiators according to the presentinvention, preferably, absorb most efficiently at this wavelength andthe mold members 78, preferably, allow maximum transmission at thiswavelength.

It is preferred that there be no sharp intensity gradients ofultraviolet radiation either horizontally or vertically through the lenscomposition during the curing process. Sharp intensity gradients throughthe lens may lead to defects in the finished lens.

According to one embodiment of the present invention, the liquid lensforming composition includes bisphenol A bis(allyl carbonate) in placeof DEG-BAC. The bisphenol A bis(allyl-carbonate) monomer has a higherrefractive index than DEG-BAC which allows the production of thinnerlenses which is important with relatively thick positive or negativelenses. The bisphenol A bis(allyl-carbonate) monomer is commerciallyavailable from PPG Industries under the trade name HIRI I or CR-73.Lenses made from this product sometimes have a very slight, barelydetectable, degree of yellowing. A small amount of a blue dye consistingof 9, 10-anthracenedione, 1-hydroxy-4-[(4-methylphenyl)amino] availableas Thermoplast Blue 684 from BASF Wyandotte Corp is preferably added tothe composition to counteract the yellowing. In addition, the yellowingtends to disappear if the lens is subjected to the above-describedpost-cure heat treatment. Moreover, if not post-cured the yellowingtends to disappear at ambient temperature after approximately 2 months.

TTEGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it is a fastpolymerizing monomer that reduces yellowing and yields a very clearproduct. If too much TTEGDA is included in the more preferredcomposition, i.e. greater than about 25% by weight, however, thefinished lens may be prone to cracking and may be too flexible as thismaterial softens at temperatures above 40 NC. If TTEGDA is excludedaltogether, the finished lens may to be brittle.

HDDMA, available from Sartomer, is a dimethacrylate monomer that has avery stiff backbone between the two methacrylate groups. HDDMA,preferably, is included in the composition because it yields a stifferpolymer and increases the hardness and strength of the finished lens.This material is quite compatible with the bisphenol A bis(allylcarbonate) monomer. HDDMA contributes to high temperature stiffness,polymer clarity and speed of polymerization.

TRPGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it providesgood strength and hardness without adding brittleness to the finishedlens. This material is also stiffer than TTEGDA.

TMPTA, available from Sartomer and Radcure, is a triacrylate monomerthat, preferably, is included in the composition because it providesmore crosslinking in the finished lens than the difunctional monomers.TMPTA has a shorter backbone than TTEGDA and increases the hightemperature stiffness and hardness of the finished lens. Moreover, thismaterial contributes to the prevention of optical distortions in thefinished lens. TMPTA also contributes to high shrinkage duringpolymerization. The inclusion of too much of this material in the morepreferred composition may make the finished lens too brittle.

Certain of the monomers that are preferably utilized in the compositionof the present invention, such as TTEGDA, TRPGDA and TMPTA, includeimpurities and have a yellow color in certain of their commerciallyavailable forms. The yellow color of these monomers is preferablyreduced or removed by passing them through a column of alumina (basic)which includes aluminum oxide powder—basic. After passage through thealumina column, the monomers absorb almost no ultraviolet light. Alsoafter passage through the alumina column differences between monomersobtained from different sources are substantially eliminated. It ispreferred, however, that the monomers be obtained from a source whichprovides the monomers with the least amount of impurities containedtherein. The composition preferably is filtered prior to polymerizationthereof to remove suspended particles.

The composition of the present invention, preferably, may be preparedaccording to the following protocol. Appropriate amounts of HDDMA,TTEGDA, TMPTA and TRPGDA are mixed and stirred thoroughly, preferablywith a glass rod. The acrylate/methacrylate mixture may then be passedthrough a purification column.

A suitable purification column may be disposed within a glass columnhaving a fitted glass disk above a teflon stopcock and having a topreservoir with a capacity of approximately 500 ml and a body with adiameter of 22 mm and a length of about 47 cm. The column may beprepared by placing on the fitted glass disk approximately 35 g. ofactivated alumina (basic), available from ALFA Products, JohnsonMatthey, Danvers, Mass. in a 60 mesh form or from Aldrich in a 150 meshform. Approximately 10 g. of an inhibitor remover(hydroquinone/methylester remover) available as HR-4 from ScientificPolymer Products, Inc., Ontario, N.Y. then may be placed on top of thealumina and, finally, approximately 35 g. of activated alumina (basic)may be placed on top of the inhibitor remover.

Approximately 600 g. of the acrylatelmethacrylate mixture may then beadded above the column packing. An overpressure of 2-3 psi may then beapplied to the top of the column resulting in a flow rate ofapproximately 30 to 38 grams per hour. Parafilm may be used to cover thejunction of the column tip and the receiving bottle to prevent theinfiltration of dust and water vapor. The acrylate/methacrylate mixture,preferably, may be received in a container that is opaque to ultravioletradiation.

An appropriate amount of bisphenol A bis(allyl carbonate) may then beadded to the acrylate/methacrylate mixture to prepare the final monomermixture.

An appropriate amount of a photoinitiator may then be added to the finalmonomer mixture. The final monomer mixture, with or withoutphotoinitiator, may then be stored in a container that is opaque toultraviolet radiation.

An appropriate amount of a dye may also be added to the final monomermixture, with or without photoinitiator.

After edging, the ultraviolet light cured lenses of the presentinvention demonstrate excellent organic solvent resistance to acetone,methylethyl ketone, and alcohols.

For best results, both the casting surfaces 86 and non-casting surfaces88 of the mold members 78 are finished to optical quality. For instance,a wave on the non-casting surface 88 may be reproduced in the finishedlens as a result of the distortion of the incident light.

Mold markings cause differential light intensity conditions under themarking, even when the mark is on the non-casting surface 88 of the moldmembers 78. The fully exposed region of the lens will tend to be harder,and the lens may have stresses because of this. The portion of the lensunder the mark will also tend to be weaker at the end of the curingperiod. This effect has been observed and may cause premature release orinduce cracking.

Mold defects at the edges interfere with the sealing conditions andfrequently induce premature release.

It is believed that as the reaction proceeds, the heat generated tendsto reduce the adhesion between the shrinking lens and the mold face.This reduction in adhesion tends to cause the lens to pull away from themold. In high curvature (i.e. high power) lenses this problem tends tobe even more pronounced because of two factors: (1) these lenses havemore thickness and thus more material that is generating heat (whichthus speeds up the reaction and generates more heat), and (2) theselenses have a greater thickness differential between the thick and thinportions of the lens, which tends to cause stress on the molds due todifferential shrinkage. It is also possible that the temperaturesgenerated relatively deep inside a thick lens may cause somevaporization of the monomer. The vaporized monomer may then migrate tothe lens/mold interface, breaking the vacuum between the two.

Because of the problem of premature release, preferably high powerlenses are cured to maintain adhesion to the molds. Preferably the moldsflex and accommodate stress.

Preferably the cooling fluid used is air at a temperature of less than50° C. The fluid may be below 0° C., however in a preferred embodimentthe fluid was at a temperature of between 0° C. and less than 20° C.,preferably about 0-15° C., more preferably about 0-10° C., morepreferably still about 3-8° C. In one preferred embodiment the fluidtemperature was about 5° C. As shown in FIG. 9, a lens forming apparatus300 for making a plastic lens may include a cooler 312 for supplyingcool fluid to the apparatus 300 via conduit 314. The fluid may besupplied to the apparatus 300 and then discharged via conduit 320. Thefluid discharged via conduit 320 may be vented via conduit 318 or it mayalternately be recirculated via conduit 316 to the cooler 312. Thecooler 312 preferably includes a Neslab CFT-50 water/antifreeze chiller(Newington, N.H., U.S.A.). A Neslab-built blower box designed for aminimum temperature of 3° C. and 8 cubic feet (about 0.224 cubic meters)per minute of air per air distributor 94 was used with the chiller. Theblower box included a heat exchanger coil through which chilled waterwas circulated, a blower, and a plenum-type arrangement for supplyingair to the conduit 314.

If lenses are produced with continuous UV light without any moldcooling, the temperature of the mold-lens assembly may rise to above 50°C. Low diopter lenses may be prepared in this fashion, but higher plusor minus diopter lenses may fail. Certain lenses may be made bycontrolling (e.g., cooling) the temperature of the lens material duringcure with circulating uncooled fluid (i.e., fluid at ambienttemperatures). The ambient fluid in these systems is directed towardsthe mold members in the same manner as described above. Circulatingambient temperature fluid permits manufacture of a wider range ofprescriptions than manufacture of the lenses without any mold cooling atall.

Most polymerization factors are interrelated. The ideal temperature ofpolymerization is related to the diopter and thickness of the lens beingcast. Thermal mass is a factor. Lower temperatures (below about 10° C.)are preferred to cast higher + or − diopter lenses when using continuousUV light. These lower temperatures tend to permit an increase inphotoinitiator concentration, which in turn may speed up the reactionand lower curing time.

Preventing premature release when using continuous UV light is alsosomewhat dependent upon the flowrates of cooling fluid, as well as itstemperature. For instance, if the temperature of the cooling fluid isdecreased it may also be possible to decrease the flowrate of coolingfluid. Similarly, the disadvantages of a higher temperature coolingfluid may be somewhat offset by higher flowrates of cooling fluid.

In one embodiment the air flow rates for a dual distributor system(i.e., an air distributor above and below the lens composition) areabout 1-30 standard cubic feet (“scf”) (about 0.028-0.850 standard cubicmeters) per minute per distributor, more preferably about 4-20 cubicfeet (about 0.113-0.566 standard cubic meters) per minute perdistributor, and more preferably still about 9-15 (about 0.255-0.423standard cubic meters) cubic feet per minute per distributor. “Standardconditions,” as used herein, means 60° F. (about 15.556° C.) and oneatmosphere pressure (about 101.325 kilopascals).

The thickness of the glass molds used to cast polymerized lenses mayaffect the lenses produced. A thinner mold tends to allow more efficientheat transfer between the polymerizing material and the cooling air,thus reducing the rate of premature release. In addition, a thinner moldtends to exhibit a greater propensity to flex. A thinner mold tends toflex during the relatively rapid differential shrinkage between thethick and thin portions of a polymerized lens, again reducing theincidence of premature release. In one embodiment the first or secondmold members have a thickness less than about 5.0 mm, preferably about1.0-5.0 mm, more preferably about 2.0-4.0 mm, and more still about2.5-3.5 mm.

“Front” mold or face means the mold or face whose surface ultimatelyforms the surface of an eyeglass lens that is furthest from the eye ofan eyeglass lens wearer. “Back” mold or face means the mold or facewhose surface ultimately forms the surface of an eyeglass lens that isclosest to the eye of a eyeglass lens wearer.

In one embodiment the lens forming material is preferably cured to forma solid lens at relatively low temperatures, relatively low continuousultraviolet light intensity, and relatively low photoinitiatorconcentrations. Lenses produced as such generally have a Shore Dhardness of about 60-78 (for preferred compositions) when cured forabout 15 minutes as described above. The hardness may be improved toabout 80-81 Shore D by postcure heating the lens in a conventional ovenfor about 10 minutes, as described above.

In a preferred embodiment, UV light may be provided with mercury vaporlamps provided in UVEXS, Inc. Model CCU or 912 curing chambers(Sunnyvale, Calif., U.S.A.).

In an alternate method for making a lens, the desired curvature (i.e.,power) of the lens may be varied using the same molds, but withdifferent light distributions. In this manner one mold may be used toprepare different lenses with different curvatures. The method includesthe steps of: (1) placing a polymerizable lens forming material in amold cavity defined in part between a first mold member and a secondmold member, and wherein the cavity defines a theoretical curvature thatis different from the desired curvature, (2) directing ultraviolet raystowards at least one of the first and second mold members, and whereinthe ultraviolet rays are directed towards the first or second moldmember such that the material cures to form a lens with the desiredcurvature, and (3) contacting fluid against the first or second moldmember to cool the first or second mold member. The resulting lenscurvature may vary depending on the way the ultraviolet light isdirected towards the first or second mold members. That is, by varyingthe relative intensity of the light across the lens material radii, itis possible to vary the curvature of the resulting lens.

EXAMPLE 1

Formulation:   17% Bisphenol A bisallyl carbonate   10% 1,6 Hexanedioldimethacrylate   20% Trimethylolpropane triacrylate   21%Tetraethyleneglycol diacrylate   32% Tripropyleneglycol diacrylate0.012% 1 Hydroxycyclohexyl phenyl ketone 0.048 Methylbenzoylformate <10PPM Hydroquinone & MethylethylhydroquinoneHydroquinone and Methylethylhydroquinone were stabilizers present insome of the diacrylate and/or triacrylate compounds obtained fromSartomer. Preferably the amount of stabilizers is minimized since thestabilizers affect the rate and amount of curing. If larger amounts ofstabilizers are added, then generally larger amounts of photoinitiatorsmust also be added.

Light Con- mW/cm² measured at plane of sample with Spectroline dition:DM 365N Meter from Spectronics Corp. (Westbury, N.Y.) Center Edge Top:0.233 0.299 Bottom: 0.217 0.248 Air Flow: 9.6 standard cubic feet(“CFM”) per manifold - 19.2 CFM total on sample Air Tem- 4.4 degreesCentigrade perature: Molds: 80 mm diameter Corning #8092 glass RadiusThickness Concave: 170.59 2.7 Convex:  62.17 5.4 Gasket: GeneralElectric SE6035 silicone rubber with a 3 mm thick lateral lip dimensionand a vertical lip dimension suffi- cient to provide an initial cavitycenter thickness of 2.2 mm. Filling: The molds were cleaned andassembled into the gasket. The mold/gasket assembly was then temporarilypositioned on a fixture which held the two molds pressed against thegasket lip with about 1 kg. of pressure. The upper edge of the gasketwas peeled back to allow about 27.4 grams of the monomer blend to becharged into the cavity. The upper edge of the gasket was then easedback into place and the excess monomer was vacuumed out with a smallaspirating device. It is preferable to avoid having monomer drip ontothe noncasting surface of the mold because a drop tends to cause theultraviolet light to become locally focused and may cause an opticaldistortion in the final product. Curing: The sample was irradiated forfifteen minutes under the above conditions and removed from the “FC-104”curing chamber (i.e., the chamber shown in FIGS. 14 and 15). The moldswere separated from the cured lens by applying a sharp impact to thejunction of the lens and the convex mold. The sample was then postcuredat 110° C. in a conventional gravity type thermal oven for an additionalten minutes, removed and allowed to cool to room tem- perature. Results:The resulting lens measured 72 mm in diameter, with a cen- tralthickness of 2.0 mm, and an edge thickness of 9.2 mm. The focusing powermeasured ˜5.05 diopter. The lens was water clear (“water-white”), showednegligible haze, exhibited total visible light transmission of about94%, and gave good overall optics. The Shore D hardness was about 80.The sample withstood the impact of a 1 inch steel ball dropped fromfifty inches in accordance with ANSI 280.1-1987, 4.6.4 test procedures.

Additional Improvements

Postcure with an Oxygen Barrier Enriched with Photoinitator

In certain applications, all of the lens forming composition may fail tocompletely cure by exposure to ultraviolet rays when forming the lens.In particular, a portion of the lens forming composition proximate thegasket often remains in a liquid state following formation of the lens.It is believed that the gaskets are often somewhat permeable to air,and, as a result, oxygen permeates them and contacts the portions of thelens forming material that are proximate the gasket. Since oxygen tendsto inhibit the photocuring process, portions of the lens formingcomposition proximate the gasket tend to remain uncured as the lens isformed.

Uncured lens forming composition proximate the gasket is a problem forseveral reasons. First, the liquid lens forming composition leaves theedges of the cured lens in a somewhat sticky state, which makes thelenses more difficult to handle. Second, the liquid lens formingcomposition is somewhat difficult to completely remove from the surfaceof the lens. Third, liquid lens forming composition may flow and atleast partially coat the surface of lenses when such lenses are removedfrom the molds. This coating is difficult to remove and makesapplication of scratch resistant coatings or tinting dyes moredifficult. This coating tends to interfere with the interaction ofscratch resistant coatings and tinting dyes with the cured lens surface.Fourth, if droplets of liquid lens forming material form, these dropletsmay later cure and form a ridge or bump on the surface of the lens,especially if the lens undergoes later postcure or scratch resistantcoating processes. As a result of the above problems, often lenses mustbe tediously cleaned or recast when liquid lens forming compositionremains after the lens is formed in an initial cure process.

The problems outlined above can be mitigated if less liquid lens formingcomposition remains proximate the gasket after the lens is formed. Onemethod of lessening this “wet edge” problem relates to increasing theamount of photoinitiator present in the lens forming composition (i.e.,increasing the amount of photoinitiator in the lens forming compositionabove about 0.15 percent). Doing so, however, tends to create otherproblems. Specifically, increased photoinitiator levels tend to causeexothermic heat to be released at a relatively high rate during thereaction of the composition. Premature release and/or lens cracking tendto result. Thus it is believed that lower amounts of photoinitiator arepreferred.

The wet edge problem has been addressed by a variety of methodsdescribed in U.S. patent application Ser. No. 07/931,946. Such methodsrelate to removing the gasket and applying either an oxygen barrier or aphotoinitiator enriched liquid to the exposed edge of the lens. The lensis then re-irradiated with sufficient ultraviolet light to completelydry the edge of the lens prior to demolding.

An embodiment of the invention relates to improving the methodsdescribed in the Ser. No. 07/931,946 application. This embodimentrelates to combining an oxygen barrier with a photoinitiator.Specifically, in one embodiment an oxygen barrier 970 (e.g., a thinstrip of polyethylene film or the like as shown in FIG. 12) is embeddedor impregnated with a photoinitiator 972. The oxygen barrier is thenwrapped around the edge of a cured lens which is still encased betweentwo molds (but with the gasket removed). While still “in the mold,” thelens is then exposed to ultraviolet light, thereby drying its edge. Animprovement of this method over those previously disclosed is that thereis a significant reduction in the UV dosage necessary to bring the lensedge to dryness.

A plastic oxygen barrier film which includes a photoinitiator may bemade by: (a) immersing a plastic film in a solution comprising aphotoinitiator, (b) removing the plastic film from the solution, and (c)drying the plastic film. The solution may include an etching agent.Preferably a surface of the plastic film is etched prior to or whileimmersing the plastic film in the solution.

In one example, thin strips (e.g., about 10 mm wide) of high densitypolyethylene film (approximately 0.013 mm thick) may be soaked in asolution of 97% acetone and 3% Irgacure 184 (a photoinitiatorcommercially available from Ciba Geigy located in Farmingdale, N.J.) forabout five minutes. The polyethylene film may be obtained from TapeSolutions, Inc. (Nashville, Tenn.). In a more preferred embodiment, 0.5%Byk 300 (a flow agent commercially available from Byk Chemie located inWallingford, Conn.) may be included in the soaking solution. It isbelieved that xylene in the Byk 300 tends to etch the surface of thefilm and make the film more receptive to absorption of the Irgacure 184.In a still more preferred embodiment, the treated polyethylene stripsmay be dipped in acetone for about ten seconds to remove excess Irgacure184. Excess photoinitiator may be seen as a white powder which coats thestrips after drying. In either case, the strips are then allowed to airdry before applying them to the edge of the lens as described above.

In one alternate embodiment of the invention, a plastic eyeglass lensmay be made by the following steps: (1) placing a liquid polymerizablelens forming composition in a mold cavity defined by a gasket, a firstmold member, and a second mold member; (2) directing first ultravioletrays toward at least one of the mold members to cure the lens formingcomposition so that it forms a lens with a back face, edges, and a frontface, and wherein a portion of the lens forming composition proximatethe edges of the lens is not fully cured; (3) removing the gasket toexpose the edges of the lens; (4) applying an oxygen barrier whichincludes a photoinitiator around the exposed edges of the lens such thatat least a portion of the oxygen barrier photoinitiator is proximatelens forming composition that is not fully cured; and (5) directingsecond ultraviolet rays towards the lens such that at least a portion ofthe oxygen barrier photoinitiator initiates reaction of lens formingcomposition while the oxygen barrier substantially prevents oxygen fromoutside the oxygen barrier from contacting at least a portion of thelens forming composition. The first and second ultraviolet rays may (a)be at the same or different wavelengths and/or intensities, (b) becontinuous or pulsed, and (c) be from the same or different lightsource.

A purpose of the steps 4-5 is to reduce the amount of uncured liquidlens forming composition that is present when the lens is separated fromthe molds and/or gasket. It has been found that reducing the amount ofliquid lens forming composition is especially advantageous if suchreduction occurs before the molds are separated from the cured lens.Separating the molds from the cured lens may cause uncured liquids to atleast partially coat the lens faces. This coating occurs because uncuredliquid lens forming composition tends to get swept over the faces whenthe molds are separated from the lens. It is believed that curing of thelens tends to create a vacuum between the lens and the mold. Air maysweep over the mold faces to fill this vacuum when the molds areseparated from the lens. This air tends to take liquid lens formingcomposition into the vacuum with it.

In step 4 above, an oxygen barrier which includes a photoinitiator isapplied to the edges or sides of the lens after the gasket is removed.Preferably this oxygen barrier is applied while the lens are stillattached to the molds. In an alternate embodiment this oxygen barrier isalso applied to the edges or sides of the molds at the same time it isapplied to the sides of the lens. In a preferred embodiment, the sidesof the lenses are first cleaned or wiped to remove at least a portion ofthe uncured liquid lens forming composition before the oxygen barrier isapplied.

After the oxygen barrier is applied, second ultraviolet rays aredirected towards the lens. After the second ultraviolet rays aredirected toward the lens, at least a portion of the liquid lens formingcomposition which was not cured in the initial cure steps is cured. Itis believed that the photoinitiator embedded in the oxygen barrierfacilitates faster and more complete curing of the uncured lens formingcomposition. As such, less second ultraviolet rays are employed, therebylessening the time and energy required in this step. Furthermore, lensquality tends to be enhanced since a lower application of the secondultraviolet rays tends to reduce the potential for lens yellowing.

In a preferred embodiment, substantially all of the remaining liquidlens forming composition is cured after the second ultraviolet rays aredirected toward the lens. More preferably, the lens is substantially dryafter the second ultraviolet rays are directed towards the lens.

After the second ultraviolet rays are directed toward the lens, the lensmay then be demolded. The lens may then be tinted. After the lens isdemolded, a scratch resistant coating may be applied to the lens. In oneembodiment, a scratch resistant coating is applied to the demolded lensby applying a liquid scratch resistant coating composition to a face ofthe lens and then applying ultraviolet rays to this face to cure theliquid scratch resistant coating to a solid.

In an embodiment, the intensity of the ultraviolet rays applied to theface of the lens to cure the liquid scratch resistant coatingcomposition to a solid is about 150-300 mW/cm² at a wave length range ofabout 360-370 nm, and about 50-150 mW/cm² at a wave length range ofabout 250-260 nm. The lens may be heated after removal from the molds,or after application of a scratch resistant coating to the lens.

In a preferred embodiment, the total intensity of the first ultravioletrays directed toward the mold members is less than about 10 mW/cm².

In an embodiment, the intensity of the second ultraviolet rays directedtoward the lens is about 150-300 mW/cm² at a wave length range of about360-370 nm, and about 50-150 mW/cm² at a wave length range of about250-260 nm. Preferably the second ultraviolet rays are directed towardsthe lens for less than about 1 minute.

In a preferred embodiment, the above method may further include theadditional step of directing third ultraviolet rays towards the lensbefore the oxygen barrier is applied. These third ultraviolet rays arepreferably applied before the gasket is removed. Preferably, the secondand third ultraviolet rays are directed toward the back face of the lens(as stated above, the second and third ultraviolet rays are preferablyapplied while this lens is in the mold cavity). The third ultravioletrays are preferably about the same range of intensity as the secondultraviolet rays. The same apparatus may be used for both the second andthird ultraviolet rays.

In a preferred embodiment, the method described above also includes thestep of removing the oxygen barrier from the edges of the lens.

The second and third ultraviolet rays may be repeatedly directed towardsthe lens. For instance, these ultraviolet rays may be applied via alight assembly whereby the lens passes under a light source on a movablestand. The lens may be repeatedly passed under the lights. Repeatedexposure of the lens to the ultraviolet rays may be more beneficial thanone prolonged exposure.

Preferably the oxygen barrier includes a film, and more preferably aplastic, flexible, and/or elastic film. In addition, the oxygen barrieris preferably at least partially transparent to ultraviolet rays so thatultraviolet rays may penetrate the oxygen barrier to cure any remainingliquid lens forming composition. Preferably the oxygen barrier isstretchable and self-sealing. These features make the film easier toapply. Preferably the oxygen barrier is resistant to penetration byliquids, thus keeping any liquid lens forming composition in the moldassembly. Preferably, the oxygen barrier includes a thermoplasticcomposition. It is anticipated that many different oxygen barriers maybe used (e.g., saran wrap, polyethylene, etc.). In one preferredembodiment, the film is “Parafilm M Laboratory Film” which is availablefrom American National Can (Greenwich, Conn., U.S.A.). The oxygenbarrier may also include aluminum foil.

Preferably the oxygen barrier is less than about 1.0 mm thick. Morepreferably the oxygen barrier is 0.01 to 0.10 mm thick, and morepreferably still the oxygen barrier is less than 0.025 mm thick. If theoxygen barrier is too thick, then it may not be readily stretchableand/or conformable, and it may not allow a sufficient amount of light topass through it. If the oxygen barrier is too thin, then it may tend totear.

An apparatus for applying a scratch resistant coating composition to alens and then curing the scratch resistant coating composition isdescribed in U.S. Pat. No. 4,895,102 to Kachel et al. and U.S. Pat. No.3,494,326 to Upton (both of which are incorporated herein by reference).In addition, the apparatus schematically shown in FIG. 10 may also beused to apply the scratch resistant coating.

FIG. 10 depicts an apparatus 600 with a first chamber 602 and a secondchamber 604. This apparatus can be used to apply scratch resistantcoating to a lens, to postcure a lens, or to apply ultraviolet light toa lens mold assembly. The first chamber 602 includes an opening 606through which an operator can apply lenses and lens mold assemblies tothe lens holder 608. Lens holder 608 is partially surrounded by barrier614. First chamber 602 may include an inspection light 610, and anopening 618 in the floor of the chamber.

Lens holder 608 is attached to device 612. It is envisioned that device612 may be a spinning device which would permit the apparatus 600 to beused to apply scratch resistant coatings to lenses. In such case device612 would connect directly to lens holder 608 through a hole in thebottom of barrier 614. In a preferred embodiment, however, device 612just connects the lens holder 608 or barrier 614 to moving device 616.It has been found that a separate spinner (not shown) may provide betterresults for application of scratch resistant coatings to lenses.

Preferably barrier 614 has an interior surface that is made or linedwith an absorbent material such as foam rubber. Preferably thisabsorbent material is disposable and removable. The absorbent materialabsorbs any liquids that fall off the lens holder 608, keeping in theinterior surface of the barrier 614 clean.

In an embodiment, shutter 621 is used to inhibit the ultraviolet lightfrom light assembly 622 from contacting barrier 614. It is preferredthat lens holder 608 be exposed to the ultraviolet light from lightassembly 622 while shutter 621 blocks at least a portion of the lightfrom contacting barrier 614. Shutter 621 may also inhibit any liquidlens forming material that falls from lens holder 606 from curing onbarrier 614. Shutter 621 thus tends to inhibit the formation of flakeson the surface of barrier 614. Shutter 621 operates after barrier 614drops, thus shielding barrier 614 while allowing UV light to contact thesample.

In an embodiment, apparatus 600 may be used to apply a precoat to lensbefore the hardcoat is applied. The precoat may serve to increase the“wettability” of the surface to which the hardcoat is to be applied. Asurfactant has been conventionally employed for this purpose, howeversurfactants tend to affect the volatility and flow characteristics oflens coatings in an unfavorable manner. The precoat may include acetoneand/or Byk 300. Upon even distribution of the hardcoat onto a lens inlens holder 608, the coating may be wiped near the edges of the lens toprevent the formation of excessive flakes during curing.

In another embodiment, the precoat and hardcoat are distributed ontolens holder 608. Ultraviolet light is directed toward the coatings atleast until a gel is formed. A lens forming material may be placed ontop of the gel and cured.

Second chamber 604 includes an opening 620 in its floor. It alsoincludes an ultraviolet light assembly 622, which may include multiplelights and a light reflector.

The apparatus 600 includes an air filtering and distribution system. Airis pulled into a chamber 628 by fans 626 through a filter 624 (thequantity and locations of the fans and filters may vary). The filteredair is distributed by the fans 626 throughout chambers 602, 604, and617. Air flows from point 613 to point 615 via air ducts (not shown) toreach chamber 617. The temperature of the lights and/or the secondchamber may be controlled by turning various fans 629 on and off asneeded to suck air out of chamber 604. Air is distributed from chamber617 through holes 636 that are proximate the lower part of the opening606 in the first chamber 602. Air is also sucked by fans 627 from thefirst chamber 602 to chamber 630 through holes 634 that are proximatethe top part of the opening 606 in the first chamber 602. Thisarrangement tends to prevent contaminants from entering first chamber606. Air is discharged from chamber 630 to the surroundings via fans627.

During use a lens or lens mold assembly may be placed on the lens holder608. A button can be pressed, causing the moving device 616 to movedevice 612, lens holder 604, and the barrier 614 so that they are underthe opening 620 in the second chamber 604. Light is thus applied to thelens or lens mold assembly from light assembly 622. After a set periodof time, the moving device 616 moves everything back to a locationunderneath the opening 618 in the first chamber 602.

The lens holder 608 may include a suction cup connected to a metal bar.The concave surface of the suction cup may be attachable to a face of amold or lens, and the convex surface of the suction cup may be attachedto a metal bar. The metal bar may be attachable to a lens spinner.

The lens holder may also alternately include movable arms and a springassembly which are together operable to hold a lens against the lensholder with spring tension during use.

In an alternate method of the invention, a lens may be cured between twomold members. The gasket may be removed and any remaining liquid lenscomposition may be removed. At this point a mold member may be appliedto a substantially solid conductive heat source. Heat may then beconductively applied to a face of the lens by (a) conductivelytransferring heat to a face of a mold member from the conductive heatsource, and (b) conductively transferring heat through such mold memberto the face of the lens. The oxygen barrier enriched with photoinitiatormay then be applied, and second ultraviolet rays may be directed towardsthe lens to cure the remaining lens forming composition.

Oxygen Barrier Example #1

A liquid lens forming composition was initially cured as in a processand apparatus similar to that specified in Example 1. The compositionwas substantially the same as specified in Example 1, with the exceptionthat hydroquinone was absent, the concentration ofmethylethylhydroquinone was about 25-45 ppm, the concentration of 1hydroxycyclohexyl phenyl ketone was 0.017 percent, and the concentrationof methylbenzoylformate was 0.068 percent. The composition underwent theinitial 15 minute cure under the “1st UV.” The apparatus wassubstantially the same as described for the above Example 1, with thefollowing exceptions:

-   -   1. The air flowrate on each side of the lens mold assembly was        estimated to be about 18-20 cubic feet per minute.    -   2. The apparatus was modified in that air flowed to and from the        openings 96 and orifices 98 (which were themselves substantially        unchanged) through a duct behind the lens forming chamber,        instead of through pipes (e.g. pipe 12 in FIG. 5). Essentially        plenum portion 95 was expanded so that the walls of the chamber        are the walls of the plenum portion 95. FIG. 14 depicts a front        view of this lens curing apparatus 800. Air in apparatus 800        flows from the orifices 98, over the lens mold assembly 802,        through ducts 804, through fan 806, through heat exchanger 808,        and then through ducts 810 and back to orifices 98 via air        return conduits 824 (shown on FIG. 15). FIG. 14 also shows a        water chiller 812 which cools water and then sends it through        conduits 814 and through heat exchanger 808. FIG. 14 also shows        lights 816 and frosted glass 818. The chamber 820 surrounding        lights 816 is not connected to the chamber 822 around the mold        assembly 802. In this manner chilled air from orifices 98 does        not contact and cool the lights 816 (such cooling tends to cause        excessive changes in light output). The chamber 820 is cooled by        fans (not shown) which turn on and off depending on the        temperature of the surface of the lights 816. FIG. 15 shows a        side view of apparatus 800.    -   3. The air flowrate in and out of the chamber surrounding the        lights was varied in accordance with the surface temperature of        lights. The air flowrate was varied in an effort to keep the        temperature on the surface of one of the lights between        104.5° F. and 105° F.    -   4. The ultraviolet light output was controlled to a set point by        varying the power sent to the lights as the output of the lights        varied.    -   5. Frosted glass was placed between the lights and the filters        used to vary the intensity of the ultraviolet light across the        face of the molds. Preferably the glass was frosted on both        sides. The frosted glass acts as a diffuser between the lights        and these filters. This frosted glass tended to yield better        results if it was placed at least about 2 mm from the filter,        more preferably about 10-15 mm, more preferably still about 12        mm, from the filter. Frosted glass was found to dampen the        effect of the filters. For instance, the presence of the frosted        glass reduced the systems' ability to produce different lens        powers by varying the light (see Example 1 and FIG. 1).    -   6. In FIG. 3 the center lights 40 are shown in a triangular        arrangement when viewed from the side. These lights were        rearranged to provide an in-line arrangement.

After initial cure, the lens mold assembly was removed from the curingchamber. The lens mold assembly included a lens surrounded by a frontmold, a back mold, and a gasket between the front and back molds (see,e.g., the assembly in FIG. 6).

At this point the protocol in Example 1 stated that the lens wasdemolded (see above). While demolding at this point is possible, asstated above generally some liquid lens forming composition remained,especially in areas of the lens proximate the gasket. Therefore the lenswas not demolded as stated in Example 1. Instead, the gasket wasremoved, liquid lens forming composition was wiped off the edges of thelens, and a layer of oxygen barrier (Parafilm M) with photoinitiator waswrapped around the edges of the lens while the lens was still betweenthe molds. The Paraflim M was wrapped tightly around the edges of thelens and then stretched so that it would adhere to the lens and molds(i.e. in a manner similar to that of Saran wrap). The lens mold assemblywas then placed in apparatus 600 so that the back face of the lens(while between the molds) could then be exposed to second ultravioletlight.

This second ultraviolet light was at a substantially higher intensitythan the initial cure light, which was directed at an intensity of lessthan 10 mW/cm². The mold assembly was passed in and out of secondchamber 604 in FIG. 10 (i.e., a UVEXS Model 912) when the light was setat the high setting. Passing in and out of the chamber took about 22seconds. The total light energy applied during these 22 seconds wasabout 4500 millijoules per square centimeter (“mJ/cm²”).

Preferably the total light energy applied per pass under the second andthird ultraviolet ray lights was in the range of about 500-10,000mJ/cm², more preferably about 3000-6000 mJ/cm², and more preferablystill 4000-5000 mJ/cm². Light energy may be varied by varying the timeof exposure, or the intensity of the light. Light energy was measuredwith a Model IL390B Light Bug from International Light, Inc.(Newburyport, Mass., U.S.A.). The total light energy represents thetotal amount of ultraviolet light over the range of 250 to 400 nm.

It has been found that applying ultraviolet light at this point helpedto cure some or all of the remaining liquid lens forming composition.The second ultraviolet light step may be repeated. In this example thesecond ultraviolet light step was repeated once. It is also possible toexpose the front or both sides of the lens to the second ultravioletlight.

After the second ultraviolet light was applied, the mold assembly wasallowed to cool. The reactions caused by exposure to ultraviolet lightare exothermic. The ultraviolet lights also tend to emit infra-red lightwhich in turn heats the mold assembly. The lens was then demolded. Thedemolded lens was substantially drier and harder than lenses that aredirectly removed from mold assemblies after the initial cure step.

Oxygen Barrier Example #2

The protocol of Oxygen Barrier Example #1 was repeated except that priorto removal of the gasket the lens mold assembly was positioned so thatthe back face of the lens was exposed to third ultraviolet light. Inthis case the third ultraviolet light was at the same intensity and forthe same time period as one pass of the second ultraviolet light. It hasbeen found that applying third ultraviolet light at this point helped tocure some or all of the remaining liquid lens forming composition sothat when the gasket was removed less liquid lens forming compositionwas present. All of the remaining steps in Oxygen Barrier Example #1were applied, and the resultant lens was substantially dry when removedfrom the molds.

Conductive Heating

An embodiment of the invention relates to postcuring a polymerized lenscontained in a mold cavity by applying conductive heat to at least oneof the molds that form the mold cavity, prior to demolding the lens.

More particularly, one embodiment of the invention includes thefollowing: (1) placing a liquid lens forming composition in a moldcavity defined by at least a first mold member and a second mold member,(2) directing ultraviolet rays toward at least one of the mold membersto cure the lens forming composition so that it forms a lens with a backface, edges, and a front face, (3) applying a mold member of the moldcavity to a substantially solid conductive heat source; and (4)conductively applying heat to a face of the lens by (a) conductivelytransferring heat to a face of a mold member from the conductive heatsource, and (b) conductively transferring heat through such mold memberto the face of the lens.

In an embodiment described as follows, a lens cured by exposure toultraviolet light is further processed by conductive heating. Suchconductive heating tends to enhance the degree of cross-linking in thelens and to increase the tintability of the lens. A lens formingmaterial is placed in mold cavity 900 (illustrated in FIG. 19), which isdefined by at least first mold member 902 and second mold member 904.Ultraviolet rays are directed toward at least one of the mold members,thereby curing the lens forming material to a lens. Heat distributor 910(shown in FIG. 16) may be adapted to distribute conductive heat fromconductive heat source 912 to at least one mold member. Heat distributor910 is preferably flexible such that at least a portion of it may beshaped to substantially conform to the shape of face 906 or face 907 offirst mold member 902 or second mold member 904, respectively. Heatdistributor 910 is preferably placed in contact with conductive heatsource 912, and mold member 902 is placed on heat distributor 910 suchthat face 906 of the mold member rests on top of the heat distributor910. Heat distributor 910 may be coupled to heat source 912. Heat isconductively applied to the heat distributor 910 by the heat source 912.Heat is conducted from the heat distributor 910 through the mold memberto a face of the lens. The heat distributor may be shaped to accommodateface 906 of first mold member 902 or face 907 of second mold member 904such that the heat is applied to front face 916 or back face 915 of thelens (shown in FIG. 11). The temperature of heat source 912 may bethermostatically controlled.

In an embodiment, hot plate 918 (shown in FIG. 17) is used as a heatsource to provide conductive heat to the lens. A number of other heatsources may be used. In an embodiment, heat distributor 910 may includecountershape 920. Countershape 920 may be placed on top of the hot plateto distribute conductive heat from the hot plate. The countershape ispreferably flexible such that at least a portion of it may substantiallyconform to the shape of an outside face of a mold member. Thecountershape may be hemispherical and either convex or concave dependingupon whether the surface of the mold assembly to be placed upon it isconvex or concave. For example, when the concave surface of the backmold is utilized to conduct heat into the lens assembly, a convexcountershape is provided to rest the assembly on.

Countershape 920 may include a glass mold, a metal optical lap, a pileof hot salt and/or sand, or any of a number of other devices adapted toconduct heat from heat source 912. It should be understood that FIG. 17includes combinations of a number of embodiments for illustrativepurposes. Any number of identical or distinct countershapes may be usedin combination on top of a heat source. In an embodiment, a countershapeincludes a container 922 filled with particles 924. The particlespreferably include metal or ceramic material. Countershape 920 mayinclude heat distributor 910. A layer 914 of material may be placed overthe countershape 920 or heat distributor 910 to provide slow, smooth,uniform heat conduction into the lens mold assembly. This layerpreferably has a relatively low heat conductivity and may be made ofrubber, cloth, Nomex™ fabric or any other suitable material thatprovides slow, smooth, uniform conduction.

In an embodiment,countershape 920 includes layer 914 (e.g., a bag orcontainer) filled with particles 924 such that the countershape may beconveniently shaped to conform to the shape of face 906 or face 907. Inan embodiment, the countershape is essentially a “beanbag” that containsparticles 924 and is conformable to the shape of a mold face placed ontop of it. Particles 924 may include ceramic material, metal material,glass beads, sand and/or salt. The particles preferably facilitateconductive heat to be applied to face 906 or face 907 substantiallyevenly.

In an embodiment, the countershape 920 is placed on top of heat source912 for a sufficient time for a portion of the countershape to attain atemperature substantially near or equal to the temperature on thesurface of the heat source. The countershape may then be “flipped over”such that the heated portion of the countershape that has a temperaturesubstantially near or equal to that of the surface of the heat source isexposed. A mold may be placed on top of the heated portion of thecountershape, and the countershape is preferably conformed to the shapeof the face of the mold. In this manner, the rate of conductive heattransfer to the lens may begin at a maximum. Heat is preferablyconductively transferred through the countershape and the mold face to aface of the lens. The temperature of the heated portion of thecountershape may tend to decrease after the mold is placed onto thecountershape.

In an embodiment, heat distributor 910 may partially insulate a moldmember from conductive heat source 912. The heat distributor preferablyallows a gradual, uniform transfer of heat to the mold member. The heatdistributor is preferably made of rubber and/or another suitablematerial. The heat distributor may include countershapes of variousshapes (e.g., hemispherically concave or convex) and sizes that areadapted to contact and receive mold members.

In an embodiment, hot plate cover 930 (shown in FIG. 8) is used todistribute conductive heat to face 906 of mold member 902. Cover 930 isadapted to rest directly upon hot plate 918 (or any other heat source).Cover 930 preferably includes portion 932, which is substantiallyconformed to the shape of face 906. Portion 932 preferably includes aconvex surface or a concave surface (not shown) adapted to receive face906. Portion 932 is preferably made of rubber and causes slow, uniformtransfer of conductive heat to face 906. In an embodiment, a hot platecover having concave indentations substantially conformed to the shapeof face 907 is used to distribute heat through a mold member to a lens.

In an embodiment, heat is conductively applied by the heat source toonly one outside face of one mold member. This outside face may be face906 or face 907. Heat may be applied to back face 915 of the lens toenhance crosslinking and/or tintability of the lens material proximateto the surface of the back face of the lens.

In a preferred embodiment, thermostatically controlled hot plate 918 isused as a heat source. Glass optical mold 928 is preferably placedconvex side up on hot plate 918 to serve as a countershape. The glassoptical mold preferably has about an 80 mm diameter and a radius ofcurvature of about 93 mm. Rubber disc 929 may be placed over this mold928 to provide uniform conductive heat to the lens mold assembly. Therubber disc is preferably made of silicone and preferably has a diameterof approximately 74 mm and a thickness of about 3 mm. The lens moldassembly preferably is placed on mold 928 so that outside face 906 of amold member of the assembly rests on top of mold 928. It is preferredthat the edge of the lens mold assembly not directly contact the hotplate. The lens mold assembly preferably receives heat through therubber disc and not through its mold edges.

To achieve good yield rates and reduce the incidence of prematurerelease while using the conductive heat method, it may be necessary forthe edge of the lens be completely cured and dry before conductive heatis applied. If the lens edge is incompletely cured (i.e., liquid or gelis still present) while conductive heat is applied, there may be a highincidence of premature release of the lens from the heating unit.

In an embodiment, the edges of a lens are treated to cure or removeincompletely cured lens forming material (see above description) beforeconductive heat is applied. The mold cavity may be defined by at leastgasket 908, first mold member 902, and second mold member 904.Ultraviolet rays are directed toward at least one of the mold members,thereby curing the lens forming material to a lens preferably havingfront face 916, a back face 915, and edges. Upon the formation of thelens, the gasket may be removed from the mold assembly. An oxygenbarrier may be used to cure any remaining liquid or gel on the lens edgeaccording to any of the methods of the above-detailed embodiments. Anoxygen barrier treated with photoinitiator is preferably employed.Alternatively, any remaining liquid or gel may be removed manually. Oncethe edge of the lens is dry, a face of the lens may be conductivelyheated using any of the methods described herein.

In an embodiment, a lens is tinted after receiving conductive heatpostcure treatment in a mold cavity. During tinting of the lens, thelens is preferably immersed in a dye solution.

Conductive Heating Example

A liquid lens forming composition was initially cured in a process andapparatus similar to that specified in Example 1 except for post-curetreatment which was conducted as follows: After the sample wasirradiated for 15 minutes, the lens was removed from the FC-104 chamberand then passed through the above-mentioned UVEXS Model 912 curingchamber (see FIG. 10) to receive a dose of about 1500 mJ/cm² (+/−100 mJ)of ultraviolet light per pass. The gasket was then removed from the moldassembly and the edges of the mold were wiped with an absorbent tissueto remove incompletely cured lens forming material proximate the moldedges. A strip of plastic material impregnated with photoinitiator waswrapped around the edges of the molds that were exposed when the gasketwas removed. Next, the mold assembly was passed through the UEXS curingchamber once to expose the front surface of the mold to a dose of about1500 mJ/cm². The mold assembly was then passed through the UVEXS fourmore times, with the back surface of the mold receiving a dose of about1500 mJ/cm² per pass. A hot plate was operated such that the surface ofthe hot plate reached a temperature of 340 degrees F. (+/−50 degreesF.). A conformable “beanbag” container having a covering made of Nomex™fabric was placed on the hot plate. The container contained glass beadsand was turned over such that the portion of the container that haddirectly contacted the hot plate (i.e., the hottest portion of thecontainer) faced upward and away from the hot plate. The mold assemblywas then placed onto the heated, exposed portion of the container thathad been in direct contact with the hot plate. The concave, non-castingface of the mold was placed onto the exposed surface of the containerwhich substantially conformed to the shape of the face. Heat wasconducted through the container and the mold member to the lens for 13minutes. A lens having a Shore D hardness of 84 was formed.

Pulsed Ultraviolet Light Application

A polymerizable lens forming composition may be placed in a mold/gasketassembly and continuously exposed to appropriate levels of ultravioletlight to cure the composition to an optical lens. The progress of thecuring reaction may be determined by monitoring the internal temperatureof the composition. The lens forming composition may be considered topass through three stages as it is cured: (1) Induction, (2) GelFormation & Exotherm, and (3) Extinction. These stages are illustratedin FIG. 20 for a −0.75-1.00 power lens cured by continuous applicationof UV light. FIG. 20 shows temperature within the mold cavity as afunction of time throughout a continuous radiation curing cycle.

The induction stage occurs at the beginning of the curing cycle and istypically characterized by a substantially steady temperature (orfalling temperature when the curing chamber temperature is below that ofthe composition) of the lens forming composition as it is irradiatedwith ultraviolet light. During the induction period, the lens formingcomposition remains in a liquid state as the photoinitiator breaks downand consumes inhibitor and dissolved oxygen present in the composition.As the inhibitor content and oxygen content of the composition fall,decomposing photoinitiator and the composition begin to form chains toproduce a pourable, “syrup-like” material.

As irradiation continues, the “syrup” proceeds to develop into a soft,non-pourable, viscous, gel. A noticeable quantity of heat will begin tobe generated during this soft gel stage. The optical quality of the lensmay be affected at this point. Should there be any sharp discontinuitiesin the intensity of the activating ultraviolet light (for example, adrop of composition on the exterior of a mold which focuses light into aportion of the lens forming composition proximate the drop), a localdistortion will tend to be created in the gel structure, likely causingan aberration in the final product. The lens forming composition willpass through this very soft gel state and through a firm gel state tobecome a crystalline structure. When using OMB-91 lens formingcomposition, a haze tends to form momentarily during the transitionbetween the gel and crystalline stages. As the reaction continues andmore double bonds are consumed, the rate of reaction and the rate ofheat generated by the reaction will slow, which may cause the internaltemperature of the lens forming composition to pass through a maximum atthe point where the rate of heat generation exactly matches the heatremoval capacity of the system.

By the time the maximum temperature has been reached and the lensforming composition begins to cool, the lens will typically haveachieved a crystalline form and will tend to crack rather than crumbleif it is broken. The rate of conversion will slow dramatically and thelens may begin to cool even though some reaction still may be occurring.Irradiation may still be applied through this extinction phase.Generally, the curing cycle is assumed to be complete when thetemperature of the lens forming composition falls to a temperature nearits temperature at the beginning of exotherm (i.e., the point where thetemperature of the composition increased due to the heat released by thereaction).

The continuous irradiation method tends to work well for relatively lowmass lenses (up to about 20-25 grams) under the FC-104 curing chamberconditions (see, e.g., U.S. Pat. Nos. 5,364,256 and 5,415,816). As theamount of material being cured increases, problems may be encountered.The total amount of heat generated during the exothermic phase issubstantially proportional to the mass of the lens forming material.During curing of relatively high mass lenses, a greater amount of heatis generated per a given time than during curing of lower mass lenses.The total mold/gasket surface area available for heat transfer (e.g.,heat removal from the lens forming composition), however, remainssubstantially constant. Thus the internal temperature of a relativelyhigh mass of lens forming material may rise to a higher temperature morerapidly than typically occurs with a lower mass of lens formingmaterial. For example, the internal temperature of a low minuscast-to-finish lens typically will not exceed about 100° F., whereascertain thicker semi-finished lens “blanks” may attain temperaturesgreater than about 350° F. when continually exposed to radiation. Thelens forming material tends to shrink as curing proceeds and the releaseof excessive heat during curing tends to reduce the adhesion between themold and the lens forming material. These factors may lead to persistentproblems of premature release and/or cracking during the curing of lensforming material having a relatively high mass.

A significant advantage of the present invention is the production ofrelatively high-mass, semi-finished lens blanks and high powercast-to-finish lenses without the above-mentioned problems of prematurerelease and cracking. Methods of the present invention as describedbelow allow even more control over the process of curing ophthalmiclenses with ultraviolet light-initiated polymerization than previousmethods. By interrupting or decreasing the activating light at theproper time during the cycle, the rate of heat generation and releasecan be controlled and the incidence of premature release can be reduced.An embodiment of the invention relates to a method of controlling therate of reaction (and therefore the rate of heat generation) of a UVlight-curable, lens forming material by applying selected intermittentdoses (e.g., pulses) of radiation followed by selected periods ofdecreased UV light or “darkness”. It is to be understood that in thedescription that follows, “darkness” refers to the absence of activatingradiation, and not necessarily the absence of visible light.

More particularly, an embodiment of the invention relates to: (a) aninitial exposure period of the lens forming material to radiation (e.g.,continuous or pulsed radiation) extending through the induction period,(b) interrupting or decreasing the irradiation before the materialreaches a first temperature (e.g., the maximum temperature thecomposition could reach if irradiation were continued) and allowing thereaction to proceed to a second temperature lower than the firsttemperature, and (c) applying a sufficient number of alternating periodsof exposure and decreased UV light or darkness to the lens formingmaterial to complete the cure while controlling the rate of heatgeneration and/or dissipation via manipulation of the timing andduration of the radiation, or the cooling in the curing chamber. FIG. 21shows the temperature within the mold cavity as a function of time forboth (a) continuous ultraviolet light exposure and (b) pulsedultraviolet light exposure.

In the context of this application, a “gel” occurs when the liquid lensforming composition is cured to the extent that it becomes substantiallynon-pourable, yet is still substantially deformable and substantiallynot crystallized.

In the following description, it is to be understood that the term“first period” refers to the length of time of the initial exposureperiod where radiation (e.g., in pulses) is applied to the lens formingcomposition, preferably to form at least a portion of the compositioninto a gel. “First ultraviolet” rays or light refers to the radiationapplied to the lens forming composition during the initial exposureperiod. “Second ultraviolet” rays or light refers to the radiation thatis applied to the lens forming composition (e.g., in pulses) after thecomposition has been allowed to cool to the “third temperature”mentioned above. “Second period” refers to the duration of time thatsecond ultraviolet rays are directed to the lens forming composition.“Third period” refers to the duration of decreased UV light or darknessthan ensues after UV light has been delivered in the second period.

In an embodiment of the invention, the lens forming material is placedin a mold cavity defined in part between a first mold member and asecond mold member. The first mold member and/or second mold member mayor may not be continuously cooled as the formation of the lens iscompleted during the second period and/or third period. One method ofremoving heat from the lens forming material is to continuously directair at a non-casting face of at least one of the mold members. It ispreferred that air be directed at both the first and second moldmembers. A cooler may be used to cool the temperature of the air to atemperature below ambient temperature, more preferably between about 0°C. and about 20° C., and more preferably still between about 3° C. andabout 15° C. Air may also be used to cool at least one of the moldmembers (in any of the manners described previously) during the firstperiod.

In an embodiment of the invention, the first period ends when at least aportion of the lens forming composition begins to increase intemperature or form a gel, and the first ultraviolet rays are decreasedor removed (e.g., blocked) such that they cease to contact the first orsecond mold members. It is preferred that the first period be sufficientto allow the lens forming material to gel in the mold cavity such thatthere is substantially no liquid present (except small amounts proximatethe edge of the material). The interruption of irradiation prior tocomplete gelation may in some circumstances produce optical distortions.It is preferred that the length of the first period be selected toinhibit the lens forming composition from reaching a first temperature.The first temperature is preferably the maximum temperature that thelens forming composition could reach if it was irradiated under thesystem conditions (e.g., flow rate and temperature of any cooling air,wavelength and intensity of radiation) until the “exothermic potential”(i.e., ability to evolve heat through reaction) of the composition wasexhausted.

According to an embodiment of the invention, the reactions within thecomposition are allowed to proceed after the first ultraviolet rays areremoved until the composition reaches a second temperature. The secondtemperature is preferably less than the first temperature. The firsttemperature is preferably never reached by the composition. Thus,preferably the composition is prevented from achieving the firsttemperature and then cooling to the second temperature. The compositionpreferably is allowed to cool from the second temperature to the thirdtemperature. This cooling may occur “inactively” by allowing heat totransfer to the ambient surroundings, or at least one of the moldmembers may be cooled by any of the methods described above.

In an embodiment of the invention, the curing of the lens formingmaterial is completed by directing second ultraviolet rays (e.g., inpulses) toward at least one of the mold members. The second UV rays maybe directed toward the mold member(s) for a second period that may bedetermined according to the rate of reaction of the lens formingcomposition. The change in temperature of the composition or a portionof the mold cavity, or the air in or exiting the chamber is an indicatorof the rate of reaction, and the second period may be determinedaccordingly. The second period may be varied such that subsequent pulseshave a longer or shorter duration than previous pulses. The time betweenpulses (i.e., the third period) may also be varied as a function of thetemperature and/or reaction rate of the composition. To achieve a lightpulse, (a) the power to a light source may be turned on and then off,(b) a device may be used to alternately transmit and then block thepassage of light to the lens forming composition, or (c) the lightsource and/or mold assembly may be moved to inhibit ultraviolet lightfrom contacting the lens forming material. The second and/or thirdperiods are preferably controlled to allow rapid formation of a lenswhile reducing the incidence of (a) premature release of the lens fromthe first and/or second mold member and/or (b) cracking of the lens.

In an embodiment, the second period is preferably controlled to inhibitthe temperature of the composition from exceeding the secondtemperature. The temperature of the lens forming composition maycontinue to increase after radiation is removed from the first and/orsecond mold members due to the exothermic nature of reactions occurringwithin the composition. The second period may be sufficiently brief suchthat the pulse of second ultraviolet rays is removed while thetemperature of the composition is below the second temperature, and thetemperature of the composition increases during the third period tobecome substantially equal to the second temperature at the point thatthe temperature of the composition begins to decrease.

In an embodiment, the third period extends until the temperature of thecomposition becomes substantially equal to the third temperature. Oncethe temperature of the composition decreases to the third temperature, apulse of second ultraviolet rays may be delivered to the composition. Inan embodiment, the second period remains constant, and the third periodis controlled to maintain the temperature of the composition below thesecond temperature. The third period may be used to lower thetemperature of the composition to a temperature that is expected tocause the composition to reach but not exceed the second temperatureafter a pulse is delivered to the composition.

In an embodiment, shutter system 950 (shown in FIG. 7) is used tocontrol the application of first and/or second ultraviolet rays to thelens forming material. Shutter system 950 preferably includesair-actuated shutter plates 954 that may be inserted into the curingchamber to prevent ultraviolet light from reaching the lens formingmaterial. Shutter system 950 may include programmable logic controller952, which may actuate air cylinder 956 to cause shutter plates 954 tobe inserted or extracted from the curing chamber. Programmable logiccontroller 952 preferably allows the insertion and extraction of shutterplates 954 at specified time intervals. Programmable logic controller952 may receive signals from thermocouple(s) located inside chamber,proximate at least a portion the mold cavity, or located to sense thetemperature of air in or exiting the chamber, allowing the timeintervals in which the shutters are inserted and/or extracted to beadjusted as a function of a temperature within the curing chamber. Thethermocouple may be located at numerous positions proximate the moldcavity and/or casting chamber.

The wavelength and intensity of the second ultraviolet rays arepreferably substantially equal to those of the first ultraviolet rays.It may be desirable to vary the intensity and/or wavelength of theradiation (e.g, first or second ultraviolet rays). The particularwavelength and intensity of the radiation employed may vary amongembodiments according to such factors as the identity of the compositionand curing cycle variables.

Numerous curing cycles may be designed and employed. The design of anoptimal cycle should include consideration of a number of interactingvariables. Significant independent variables include: 1) the mass of thesample of lens forming material, 2) the intensity of the light appliedto the material, 3) the physical characteristics of the lens formingmaterial, and 4) the cooling efficiency of the system. Significantcuring cycle (dependent) variables include: 1) the optimum initialexposure time for induction and gelling, 2) the total cycle time, 3) thetime period between pulses, 4) the duration of the pulses, and 5) thetotal exposure time.

Most of the experiments involving methods of the present invention wereconducted using below described OMB-91 monomer and the above-mentionedFC-104 curing chamber set at an operating temperature of 55 degrees F.,although tests have been performed using other lens forming materialsand curing chamber temperatures. The OMB-91 formulation and propertiesare listed below.

OMB-91 FORMULATION: INGREDIENT WEIGHT PERCENT Sartomer SR 351(Trimethylolpropane 20.0 +/− 1.0 Triacrylate) Sartomer SR 268(Tetraethylene Glycol 21.0 +/− 1.0 Diacrylate) Sartomer SR 306(Tripropylene Glycol 32.0 +/− 1.0 Diacrylate) Sartomer SR 239 (1,6Hexanediol 10.0 +/− 1.0 Dimethacrylate) (Bisphenol A Bis(AllylCarbonate)) 17.0 +/− 1.0 Irgacure 184 (1-Hydroxycyclohexyl 0.017 +/−0.0002 Phenyl Keytone) Methyl Benzoyl Formate 0.068 +/− 0.0007 MethylEster of Hydroquinone (“MeHQ”)   35 ppm +/−  10 ppm Thermoplast Blue P(9,10 - 0.35 ppm +/− 0.1 ppm Anthracenedione, 1-hydroxy-4-((4-methylphenyl) Amino) MEASUREMENTS/PROPERTIES: PROPERTY PROPOSED SPECIFICATIONAppearance Clear Liquid Color (APHA) 50 maximum (Test Tube Test) MatchStandard Acidity (ppm as Acrylic Acid) 100 maximum Refractive Index1.4725 +/− 0.002 Density 1.08 +/− 0.005 gm/cc. at 23 degrees C.Viscosity @ 22.5 Degrees C. 27.0 +/− 2 centipoise Solvent Weight (wt %)0.1 Maximum Water (wt %) 0.1 Maximum MeHQ (from HPLC) 35 ppm +/− 10 ppm

It is recognized that methods and systems of the present invention couldbe applied to a large variety of radiation-curable, lens formingmaterials in addition to those mentioned herein. It should be understoodthat adjustments to curing cycle variables (particularly the initialexposure time) may be required even among lens forming compositions ofthe same type due to variations in inhibitor levels among batches of thelens forming compositions. In addition, changes in the heat removalcapacity of the system may require adjustments to the curing cyclevariables (e.g. duration of the cooling periods between radiationpulses). Changes in the cooling capacity of the system and/or changes incompositions of the lens forming material may require adjustments tocuring cycle variables as well.

Significant variables impacting the design of a pulsed curing cycleinclude (a) the mass of the material to be cured and (b) the intensityof the light applied to the material. A significant aspect of methods ofthe present invention is the initial exposure period. If a sample isinitially overdosed with radiation, the reaction may progress too farand increase the likelihood of premature release and/or cracking. If asample is underdosed initially in a fixed (i.e., preset) curing cycle,subsequent exposures may cause too great a temperature rise later in thecycle, tending to cause premature release and/or cracking. Additionally,if the light intensity varies more than about +/−10% in a cycle that hasbeen designed for a fixed light intensity level and/or fixed mass oflens forming material, premature release and/or cracking may result.

An embodiment of the present invention involves a curing cycle havingtwo processes. A first process relates to forming a dry gel bycontinuously irradiating a lens forming composition for a relativelylong period. The material is then cooled down to a lower temperatureunder darkness. A second process relates to controllably discharging theremaining exothermic potential of the material by alternately exposingthe material to relatively short periods of irradiation and longerperiods of decreased irradiation (e.g., dark cooling).

The behavior of the lens forming material during the second process willdepend upon the degree of reaction of the lens forming material that hasoccurred during the first process. For a fixed curing cycle, it ispreferable that the extent of reaction occurring in the first processconsistently fall within a specified range. If the progress of reactionis not controlled well, the incidence of cracking and/or prematurerelease may rise. For a curing cycle involving a composition having aconstant level of inhibitor and initiator, the intensity of theradiation employed is the most likely source of variability in the levelof cure attained in the first process. Generally, a fluctuation of +/−5%in the intensity tends to cause observable differences in the cure levelachieved in the first process. Light intensity variations of +/−10% maysignificantly reduce yield rates.

The effect of various light intensities on the material being cureddepends upon whether the intensity is higher or lower than a preferredintensity for which the curing cycle was designed. FIG. 23 showstemperature profiles for three embodiments in which different lightlevels were employed. If the light intensity to which the material isexposed is higher than a preferred intensity, the overdosage may causethe reaction to proceed too far. In such a case, excessive heat may begenerated, increasing the possibility of cracking and/or prematurerelease during the first process of the curing cycle. If prematurerelease or cracking of the overdosed material does not occur in thefirst process, then subsequent pulses administered during the secondprocess may create very little additional reaction.

If the light intensity is lower than a preferred intensity and the lensforming material is underdosed, other problems may arise. The materialmay not be driven to a sufficient level of cure in the first process.Pulses applied during the second process may then cause relatively highamounts of reaction to occur, and the heat generated by reaction may bemuch greater than the heat removal capacity of the system. Thus thetemperature of the lens forming material may tend to excessivelyincrease. Premature release may result. Otherwise, undercured lensesthat continue generating heat after the end of the cycle may beproduced.

The optimal initial radiation dose to apply to the lens forming materialmay depend primarily upon its mass. The initial dose is also a functionof the light intensity and exposure time. A method for designing acuring cycle for a given mold/gasket/monomer combination may involveselecting a fixed light intensity.

Methods of the present invention may involve a wide range of lightintensities. Using a relatively low intensity may allow for the lengthof each cooling step to be decreased such that shorter and morecontrollable pulses are applied. Where a fluorescent lamp is employed,the use of a lower intensity may allow the use of lower power settings,thereby reducing the load on the lamp cooling system and extending thelife of the lamp. A disadvantage of using a relatively low lightintensity is that the initial exposure period tends to be somewhatlonger. Relatively high intensity levels tend to provide shorter initialexposure times while placing more demand upon the lamp drivers and/orlamp cooling system, either of which tends to reduce the life of thelamp.

In an embodiment, General Electric F15T8BL lamps powered by MercronHR0696-4 drivers may be used in conjunction with an FC 104 curingchamber having one piece of double-frosted diffusing glass and one pieceof clear P0-4 acrylic plate. The light intensity settings may be 760microwatts/cm² for the top lamps and 950 microwatts/cm² for the bottomlamps.

Once a light intensity is selected, the initial exposure time may bedetermined. A convenient method of monitoring the reaction during thecycle involves fashioning a fine gage thermocouple, positioning itinside the mold cavity, and connecting it to an appropriate dataacquisition system. A preferred thermocouple is Type J, 0.005 inchdiameter, Teflon-insulated wire available from Omega Engineering. Theinsulation is stripped back about 30 to 50 mm and each wire is passedthrough the gasket wall via a fine bore hypodermic needle. The needle isthen removed and the two wires are twisted together to form athermocouple junction inside the inner circumference of the gasket. Theother ends of the leads are attached to a miniature connector which canbe plugged into a permanent thermocouple extension cord leading to thedata acquisition unit after the mold set is filled.

The data acquisition unit may be a Hydra 2625A Data Logger made by JohnFluke Mfg. Company. It is connected to an IBM compatible personalcomputer running Hydra Data Logger software. The computer is configuredto display a trend plot as well as numeric temperature readings on amonitor. The scan interval may be set to any convenient time period anda period of five or ten seconds usually provides good resolution.

The position of the thermocouple junction in the mold cavity may affectits reading and behavior through the cycle. When the junction is locatedbetween the front and back molds, relatively high temperatures may beobserved compared to the temperatures at or near the mold face. Thedistance from the edge of the cavity to the junction may affect bothabsolute temperature readings as well as the shape of the curing cycles'temperature plot. The edges of the lens forming material may begin toincrease in temperature slightly later than other portions of thematerial. Later in the cycle, the lens forming material at the centermay be somewhat ahead of the material at the edge and will tend torespond little to the radiation pulses, whereas the material near theedge may tend to exhibit significant activity. When performingexperiments to develop curing cycles, it is preferred to insert twoprobes into the mold cavity, one near the center and one near the edge.The center probe should be relied upon early in the cycle and the edgeprobe should guide the later stages of the cycle.

Differing rates of reaction among various regions of the lens formingmaterial may be achieved by applying a differential light distributionacross the mold face(s). Tests have been performed where “minus type”light distributions have caused the edge of the lens forming material tobegin reacting before the center of the material. The potentialadvantages of using light distributing filters to cure high masssemi-finished lenses may be offset by nonuniformity of total lighttransmission that tends to occur across large numbers of filters. The UVlight transmission of the PO-4 acrylic plates (Cyro Industries; Plano,Tex.) used over the apertures in the FC-104 curing chamber tends to beconsiderably more consistent than that of silk-screened filter plates.

After the selection and/or configuration of (a) the radiation intensity,(b) the radiation-curable, lens forming material, (c) the mold/gasketset, and (d) the data acquisition system, the optimum initial exposureperiod may be determined. It is useful to expose a sample of lensforming material to continuous radiation to obtain a temperatureprofile. This will provide an identifiable range of elapsed time withinwhich the optimal initial exposure time will fall. Two points ofinterest are the time where the temperature rise in the sample is firstdetected (“T initial” or “Ti”), and the time where the maximumtemperature of the sample is reached (“Tmax”). Also of interest is theactual maximum temperature, an indication of the “heat potential” of thesample under the system conditions (e.g., in the presence of cooling).

As a general rule, the temperature of high mass lenses (i.e., lensesgreater than about 70 grams) should remain under about 200° F. andpreferably between about 150° F. and about 180° F. Higher temperaturesare typically associated with reduced lens yield rates due to crackingand/or premature release. Generally, the lower mass lenses (i.e., lensesno greater than about 45 grams) should be kept under about 150° F. andpreferably between about 110° F. and about 140° F.

The first period may be selected according to the mass of the lensforming material. In an embodiment, the lens forming material has a massof between about 45 grams and about 70 grams and the selected secondtemperature is a temperature between about 150° F. and about 200° F.According to another embodiment, the lens forming material has a mass nogreater than about 45 grams and a second temperature less than about150° F. In yet another embodiment of the invention, the lens formingmaterial has a mass of at least about 70 grams, and a second temperaturebetween about 170° F. and about 190° F.

An experiment may be performed in which the radiation is removed fromthe mold members slightly before one-half of the time between T initialand Tmax. The initial exposure time may be iteratively reduced orincreased according to the results of the above experiment in subsequentexperiments to provide a Tmax in a preferred range. This procedure mayallow the determination of the optimal initial exposure time for anygiven mold/gasket set and light intensity.

A qualitative summary of relationships among system variables related tothe above-described methods is shown in FIG. 22.

After the initial exposure period, a series of irradiation pulse/coolingsteps may be performed to controllably discharge the remainingexothermic potential of the material and thus complete the cure. Thereare at least two approaches to accomplish this second process. The firstinvolves applying a large number of very short pulses and short coolingperiods. The second approach involves applying a fewer number of longerpluses with correspondingly longer cooling periods. Either of these twomethods may produce a good product and many acceptable cycles may existbetween these extremes.

A significant aspect of the invention relates to using pulsedapplication of light to produce a large range (e.g., from −6 to +4diopter) of lenses without requiring refrigerated cooling fluid (e.g.,cooled air). With proper light application, air at ambient may be usedas a cooling fluid, thus significantly reducing system costs.

Some established cycles are detailed in the table below for threesemifinished mold gasket sets: a 6.00 D base curve, a 4.50 D base curve,and a 3.00 D base curve. These cycles have been performed using anFC-104 curing chamber in which cooling air at a temperature of about 56degrees F. was directed at the front and back surfaces of a moldassembly. Frosted diffusing window glass was positioned between thesamples and the lamps, with a layer of PO-4 acrylic materialapproximately 1 inch below the glass. A top light intensity was adjustedto 760 microwatts/cm² and a bottom light intensity was adjusted to 950microwatts/cm², as measured at about the plane of the sample. ASpectroline meter DM365N and standard detector stage were used. Anin-mold coating as described in U.S. application Ser. No. 07/931,946 wasused to coat both the front and back molds.

BASE CURVE 6.00 4.50 3.00 Mold Sets Front Mold 5.95 4.45 2.93 Back Mold6.05 6.80 7.80 Gasket −5.00 13 mm 16 mm Resulting Semifinished BlankDiameter 74 mm 76 mm 76 mm Center Thickness 9.0 mm 7.8 mm 7.3 mm EdgeThickness 9.0 mm 11.0 mm 15.0 mm Mass 46 grams 48 grams 57 grams CuringCycle Vari- ables Total Cycle Time 25:00 25:00 35:00 Initial Exposure 4:40  4:40  4:35 Number of Pulses 4 4 4 Timing (in sec- onds) andDuration of Pulses @ Elapsed Time From Onset of Initial Exposure Pulse 115@10:00 15@10:00 15@13:00 Pulse 2 15@15:00 15@15:00 15@21:00 Pulse 330@19:00 30@19:00 20@27:00 Pulse 4 30@22:00 30@22:00 30@32:00

FIGS. 24, 25, and 26 each show temperature profiles of theabove-detailed cycles for a case where the ultraviolet light exposure iscontinuous and a case where the ultraviolet light delivery is pulsed. InFIGS. 23-26, “Io” denotes the initial intensity of the ultraviolet raysused in a curing cycle. The phrase “Io=760/950” means that the lightintensity was adjusted to initial settings of 760 microwatts/cm² for thetop lamps and 950 microwatts/cm² for the bottom lamps. The “interiortemperature” of FIGS. 23-26 refers to a temperature of the lens formingmaterial as measured by a thermocouple located within the mold cavity.

The following general rules for the design of pulse/cooling cycles maybe employed to allow rapid curing of a lens while inhibiting prematurerelease and/or cracking of the lens. The duration of the pulsespreferably does not result in a temperature that exceeds the maximumtemperature attained in the initial exposure period. The length of thecooling period may be determined by the length of time necessary for theinternal temperature of the lens forming material to return to near thetemperature it had immediately before it received a pulse. Followingthese general rules during routine experimentation may permit propercuring cycles to be established for a broad range of lens formingmaterials, light intensity levels, and cooling conditions.

Preferably light output is measured and controlled by varying the amountof power applied to the lights in response to changes in light output.Specifically, a preferred embodiment of the invention includes a lightsensor mounted near the lights. This light sensor measures the amount oflight, and then a controller increases the power supplied to maintainthe first ultraviolet rays as the intensity of the first ultravioletrays decreases during use, and vice versa. Specifically, the power isvaried by varying the electric frequency supplied to the lights.

A filter is preferably applied to the light sensor so that light wavesother than ultraviolet light impinge less, or not at all, on the lightsensor. In one embodiment, a piece of 365N Glass made by Hoya Optics(Fremont, Calif.) was applied to a light sensor to filter out visiblerays.

One “lamp driver” or light controller was a Mercron Model FX0696-4 andModel FX06120-6 (Mercron, Inc., Dallas, Tex. U.S.A.). These lightcontrollers may be described in U.S. Pat. Nos. 4,717,863 and 4,937,470.

FIG. 13 schematically depicts the light control system described above.The lights 40 in apparatus 10 apply light towards the lens holder 70. Alight sensor 700 is located adjacent the lights 40. Preferably the lightsensor 700 is a photoresistor light sensor (photodiodes or other lightsensors may also be usable in this application). The light sensor 700with a filter 750 is connected to lamp driver 702 via wires 704. Lampdriver 702 sends a current through the light sensor 700 and receives areturn signal from the light sensor 700. The return signal is comparedagainst an adjustable set point, and then the electrical frequency sentto the ultraviolet lights 40 via wires 706 is varied depending on thedifferences between the set point and the signal received from the lightsensor 700. Preferably the light output is maintained within about+/−1.0 percent.

In an embodiment of the invention, a medium pressure mercury vapor lampis used to cure the lens forming material and the lens coating. Thislamp and many conventional light sources used for ultraviolet lightcuring may not be repeatedly turned on and off since a several minutewarm-up period is generally required prior to operation. Mercury vaporlight sources may be idled at a lower power setting between exposureperiods (i.e., second periods), however, the light source will stillgenerate significant heat and consume electricity while at the lowerpower setting.

In an embodiment, a flash lamp emits ultraviolet light pulses to curethe lens forming material. It is believed that a flash lamp wouldprovide a smaller, cooler, less expensive, and more reliable lightsource than other sources. The power supply for a flash lamp tends todraw relatively minimal current while charging its capacitor bank. Theflash lamp discharges the stored energy on a microsecond scale toproduce very high peak intensities from the flash tube itself. Thusflash lamps tend to require less power for operation and generate lessheat than other light sources used for ultraviolet light curing. A flashlamp may also be used to cure a lens coating.

In an embodiment, the flash lamp used to direct ultraviolet rays towardat least one of the mold members is a xenon light source. The lenscoating may also be cured using a xenon light source. Referring to FIG.29, xenon light source 980 preferably contains photostrobe 992 having atube 996 and electrodes to allow the transmission of ultraviolet rays.The tube may include borosilicate glass or quartz. A quartz tube willgenerally withstand about 3 to 10 times more power than a hard glasstube. The tube may be in the shape of a ring, U, helix, or it may belinear. The tube may include capacitive trigger electrode 995. Thecapacitive trigger electrode may include a wire, silver strip, orconductive coating located on the exterior of tube 996. The xenon lightsource is preferably adapted to deliver pulses of light for a durationof less than about 1 second, more preferably between about 1/10 of asecond and about 1/1000 of a second, and more preferably still betweenabout 1/400 of a second and 1/600 of a second. The xenon source may beadapted to deliver light pulses about every 4 seconds or less. Therelatively high intensity of the xenon lamp and short pulse duration mayallow rapid curing of the lens forming composition without impartingsignificant radiative heat to the composition.

In an embodiment, controller 990 (shown in FIG. 29) controls theintensity and duration of ultraviolet light pulses delivered fromultraviolet light source 980 and the time interval between pulses.Ultraviolet light source 980 may include capacitor 994, which stores theenergy required to deliver the pulses of ultraviolet light. Capacitor994 may be adapted to allow pulses of ultraviolet light to be deliveredas frequently as desired. Temperature monitor 997 may be located at anumber of positions within mold chamber 984. The temperature monitor maymeasure the temperature within the chamber and/or the temperature of airexiting the chamber. The system may be adapted to send a signal tocooler 988 and/or distributor 986 (shown in FIG. 27) to vary the amountand/or temperature of the cooling air. The temperature monitor may alsodetermine the temperature at any of a number of locations proximate themold cavity and send a signal to controller 990 to vary the pulseduration, pulse intensity, or time between pulses as a function of atemperature within mold chamber 984.

In an embodiment, light sensor 999 is used to determine the intensity ofultraviolet light emanating from source 980. The light sensor ispreferably adapted to send a signal to controller 990, which ispreferably adapted to maintain the intensity of the ultraviolet light ata selected level. Filter 998 may be positioned between ultraviolet lightsource 980 and light sensor 999 and is preferably adapted to inhibitvisible rays from contacting light sensor 999, while allowingultraviolet rays to contact the sensor. The filter may include 365 Nglass or any other material adapted to filter visible rays and transmitultraviolet rays.

In an embodiment, a cooling distributor is used to direct air toward thenon-casting face of at least one of the mold members to cool the lensforming composition. The air may be cooled to a temperature of belowambient temperature prior to being directed toward at least one of themold members to cool the composition.

In an embodiment, air at ambient temperature may be used to cool thelens forming composition. Since the xenon flash generally has a durationof much less than about one second, considerably less radiative heattends to be transferred to the lens forming composition compared tocuring methods employing other ultraviolet sources. Thus, the reducedheat imparted to the lens forming composition may allow for air atambient temperature to remove sufficient heat of exotherm tosubstantially inhibit premature release and/or cracking of the lens.

In an embodiment, the xenon source is used to direct first ultravioletrays toward the first and second mold members to the point that atemperature increase is measured and/or the lens forming compositionbegins to or forms a gel. It is preferred that the gel is formed withless than 15 pulses of radiation, and more preferably with less thanabout 5 pulses. It is preferred that the gel is formed before the totaltime to which the composition has been exposed to the pulses exceedsabout 1/10 or 1/100 of a second.

In an embodiment, a reflecting device is employed in conjunction withthe xenon light source. The reflecting device is positioned behind theflash source and preferably allows an even distribution of ultravioletrays from the center of the composition to the edge of the composition.

In an embodiment, a xenon light flash lamp is used to apply a pluralityof ultraviolet light pulses to the lens forming composition to cure itto an eyeglass lens in a time period of less than 30 minutes, or morepreferably, less than 20 or 15 minutes.

The use of a xenon light source also may allow the formation lenses overa wider range of diopters. Higher power lenses exhibit greatest thinnestto thickest region ratios, meaning that more shrinkage-induced stress iscreated, causing greater mold flexure and thus increased tendency forpremature release. Higher power lenses also possess thicker regions.Portions of lens forming material within these thicker regions mayreceive less light than regions closer to the mold surfaces. Continuousirradiation lens forming techniques typically require the use ofrelatively low light intensities to control the heat generated duringcuring. The relatively low light intensities used tends to result in along, slow gelation period. Optical distortions tend to be created whenone portion of the lens is cured at a different rate than anotherportion. Methods characterized by non-uniform curing are typicallypoorly suited for the production of relatively high power lenses, sincethe deeper regions (e.g., regions within a thick portion of a lens) tendto gel at a slower rate than regions closer to the mold surfaces.

The relatively high intensity attainable with the xenon source may allowdeeper penetration into, and/or saturation of, the lens forming materialthereby allowing uniform curing of thicker lenses than in conventionalradiation-initiated curing. More uniform gelation tends to occur wherethe lens forming material is dosed with a high intensity pulse ofultraviolet light and then subjected to decreased UV light or darknessas the reaction proceeds without activating radiation. Lenses having adiopter of between about +5.0 and about −6.0 and greater may be cured.It is believed that light distribution across the sample is lesscritical when curing and especially when gelation is induced withrelatively high intensity light. The lens forming material may becapable of absorbing an amount of energy per time that is below thatdelivered during a relatively high intensity pulse. The lens formingmaterial may be “oversaturated” with respect to the light delivered viaa high intensity flash source. In an embodiment, the xenon source isused to cure a lens having a diopter between about −4.0 and about −6.0.In an embodiment, the xenon source is used to cure a lens having adiopter between about +2.0 and about +4.0.

In an embodiment, more than one xenon light source is usedsimultaneously to apply ultraviolet pulses to the lens formingcomposition. Such an embodiment is shown in FIG. 28. Xenon light sources980 a and 980 b may be positioned around mold chamber 985 so that pulsesmay be directed toward the front face of a lens and the back face of alens substantially simultaneously. Mold chamber 985 is preferablyadapted to hold a mold in a vertical position such that pulses fromxenon source 980 a may be applied to the face of a first mold member,while pulses from source 980 b may be applied to the face of a secondmold member. In an embodiment, xenon source 980 b applies ultravioletlight pulses to a back surface of a lens more frequently than xenonsource 980 a applies ultraviolet light pulses to a front surface of alens. Xenon sources 980 a and 980 b may be configured such that onesource applies light to mold chamber 984 from a position above thechamber while the other xenon source applies light to the mold chamberfrom a position below the chamber.

In an embodiment, a xenon light source and a relatively low intensity(e.g., fluorescent) light source are used to simultaneously applyultraviolet light to a mold chamber. As illustrated in FIG. 27, xenonsource 980 may apply ultraviolet light to one side of mold chamber 984while low intensity fluorescent source 982 applies ultraviolet light toanother side of the mold chamber. Fluorescent source 982 may include acompact fluorescent “light bucket” or a diffused fluorescent lamp. Thefluorescent light source may deliver continuous or substantially pulsedultraviolet rays as the xenon source delivers ultraviolet pulses. Thefluorescent source may deliver continuous ultraviolet rays having arelatively low intensity of less than about 100 microwatts/cm².

Methods of the present invention allow curing of high-mass semi-finishedlens blanks from the same material used to cure cast-to-finish lenses.Both are considered to be “eyeglass lenses” for the purposes of thispatent. These methods may also be used to cure a variety of other lensforming materials. Methods of the present invention have beensuccessfully used to make cast-to-finish lenses in addition tosemi-finished lenses.

Pulse Method Example 1

Use of a Medium Pressure Vapor Lamp

An eyeglass lens was successfully cured with ultraviolet light utilizinga medium pressure mercury vapor lamp as a source of activating radiation(i.e., the UVEXS Model 912 previously described herein). The curingchamber included a six inch medium pressure vapor lamp operating at apower level of approximately 250 watts per inch and a defocused dichroicreflector that is highly UV reflective. A high percentage of infraredradiation was passed through the body of the reflector so that it wouldnot be directed toward the material to be cured. The curing chamberfurther included a conveyer mechanism for transporting the sampleunderneath the lamp. With this curing chamber, the transport mechanismwas set up so that a carriage would move the sample from the front ofthe chamber to the rear such that the sample would move completelythrough an irradiation zone under the lamp. The sample would then betransported through the zone again to the front of the chamber. In thismanner the sample was provided with two distinct exposures per cycle.One pass, as defined hereinafter, consists of two of these distinctexposures. One pass provided a dosage of approximately 275 milliJoulesmeasured at the plane of the sample using an International Light IL 1400radiometer equipped with a XRL 340 B detector.

A lens cavity was created using the same molds lens forming composition,and gasket of Pulsed Method Example 2 below. The reaction cellcontaining the lens forming material was placed on a supporting stagesuch that the plane of the edges of the convex mold were at a distanceof approximately 75 mm from the plane of the lamp. The lens cavity wasthen exposed to a series of UV doses consisting of two passes directedto the back surface of the mold followed immediately by one passdirected to the front surface of the mold. Subsequent to these firstexposures, the reaction cell was allowed to cool for 5 minutes in theabsence of any activating radiation in an FC-104 chamber as described inPulsed Method Example 1 at an air temperature of 74.6 degrees F. and atan air flow rate of approximately 15 to 25 scf per minute to the backsurface and 15 to 25 scf to the front surface of the cell. The lenscavity was then dosed with one pass to the front mold surface andreturned to the cooling chamber for 6 minutes. Then the back surface wasexposed in one pass and then was cooled for 2 minutes. Next, the frontsurface was exposed in two passes and then cooled for 3.5 minutes. Thefront surface and the back surface were then each exposed to two passes,and the gasket was removed to expose the edges of the lens. A strip ofpolyethylene film impregnated with photoinitiator was then wrappedaround the edge of the lens and the front and back surfaces were exposedto another 3 passes each. The back surface of the cell was then placedon the conductive thermal in-mold postcure device using “bean-bag”container filled with glass beads on a hot plate at about 340° F.described previously (see conductive heating example 1) for a timeperiod of 13 minutes, after which the glass molds were removed from thefinished lens. The finished lens exhibited a distance focusing power of−6.09 diopters, had excellent optics, was aberration-free, was 74 mm indiameter, and had a center thickness of 1.6 mm. During the coolingsteps, a small surface probe thermistor was positioned against theoutside of the gasket wall to monitor the reaction. The results aresummarized below.

Approx. Elapsed Gasket Wall Time After UV Dose Temperature UV Dose (min)(° F.) 2 passes to back surface and 0 Not recorded 1 pass to frontsurface 1 80.5 2 79.7 3 79.0 4 77.1 5 76.2 1 pass to front surface 0 Notrecorded 1 83.4 2 86.5 3 84.6 4 Not recorded 5 81.4 6 79.5 1 pass toback surface 0 Not recorded 1 79.3 2 79.0 2 passes to front surface 0Not recorded 1 78.4 2 77.8 3 77.0 3.5 76.7

Pulse Method Example 2

Use of a Single Xenon Flash Lamp

An eyeglass lens was successfully cured with ultraviolet light utilizinga xenon flash lamp as a source of activating radiation. The flash lampused was an Ultra 1800 White Lightning photographic strobe, commerciallyavailable from Paul C. Buff Incorporated of Nashville, Tenn. This lampwas modified by replacing the standard borosilicate flash tubes withquartz flash tubes. A quartz flash tube is preferred because some of theultraviolet light generated by the arc inside the tube tends to beabsorbed by borosilicate glass. The strobe possessed two semicircularflash tubes that trigger simultaneously and are positioned to form aring approximately 73 millimeters in diameter. The hole in the reflectorbehind the lamps, which normally contains a modeling lamp forphotographic purposes, was covered with a flat piece of highly-polishedultraviolet reflective material, which is commercially available underthe trade name of Alzac from Ultra Violet Process Supply of Chicago,Ill. The power selector switch was set to fill power. The ultravioletenergy generated from one flash was measured using an InternationalLight IL 1700 Research Radiometer available from International Light,Incorporated of Newburyport, Mass. The detector head was anInternational Light XRL 340 B, which is sensitive to radiation in the326 nm to 401 nm region. The window of the detector head was positionedapproximately 35 mm from the plane of the flash tubes and wasapproximately centered within the ring formed by the tubes.

A mold cavity was created by placing two round 80 mm diameter crownglass molds into a silicone rubber ring or gasket, which possessed araised lip around its inner circumference. The edges of the glass moldsrested upon the raised lip to form a sealed cavity in the shape of thelens to be created. The inner circumference of the raised lipcorresponded to the edge of the finished lens. The concave surface ofthe first mold corresponded to the front surface of the finished lensand the convex surface of the second mold corresponded to the backsurface of the finished lens. The height of the raised lip of the rubberring into which the two glass molds are inserted controls the spacingbetween the two glass molds, thereby controlling the thickness of thefinished lens. By selecting proper gaskets and first and second moldsthat possess various radii of curvature, lens cavities can be created toproduce lenses of various powers.

A lens cavity was created by placing a concave glass mold with a radiusof curvature of 407.20 mm and a convex glass mold with a radius ofcurvature of 65.26 mm into a gasket which provided spacing between themolds of 1.8 mm measured at the center of the cavity. Approximately 32grams of a lens forming monomer was charged into the cavity. The lensforming material used for this test was OMB-91 lens monomer. Thereaction cell containing the lens forming material was placedhorizontally on a supporting stage such that the plane of the edges ofthe convex mold were at a distance of approximately 30 mm from the planeof the flash tubes and the cell was approximately centered under thelight source.

The back surface of the lens cavity was then exposed to a first seriesof 5 flashes, with an interval of approximately 4 seconds in betweeneach flash. The cell was then turned over and the front surface wasexposed to another 4 flashes with intervals of about 4 seconds inbetween each flash. It is preferable to apply the first set of flashesto the back surface to start to cure the material so that any airbubbles in the liquid monomer will not migrate from the edge of thecavity to the center of the optical zone of the lens. Subsequent tothese first nine flashes, the reaction cell was allowed to cool for fiveminutes in the absence of any activating radiation in theabove-described FC-104 chamber. To cool the reaction cell, air at atemperature of71.4 degrees F. and at a flow rate of approximately 15 to25 scf per minute was applied to the back surface and air at atemperature of 71.4 degrees F. and at a flow rate of approximately 15 to25 scf per minute was applied to the front surface of the cell. The backsurface of the lens cavity was then dosed with one more flash andreturned to the cooling chamber for four minutes.

Next, the cell was exposed to one flash on the front surface and cooledin the cooling chamber for seven minutes. Then the cell was exposed toone flash on the front surface and one flash on the back surface andcooled for three minutes. Next, the cell was exposed to two flashes onthe front surface and two flashes on the back surface and cooled forfour and a half minutes. The cell was then exposed to five flashes eachto the back surface and front surface, and the gasket was removed toexpose the edges of the lens. A strip of polyethylene film impregnatedwith photoinitiator (Irgacure 184) was then wrapped around the edge ofthe lens, and the cell was exposed to another five flashes to the frontsurface and fifteen flashes to the back surface. The back surface of thecell was then placed on the conductive thermal in-mold postcure device(i.e., “bean bags” filled with glass beads sitting on a hot plate atapprox. 340° F.) as described previously (see conductive heating exampleabove) for a time period of 13 minutes, after which the glass molds wereremoved from the finished lens. The finished lens exhibited a distancefocusing power of −6.16 diopters and a +2.55 bifocal add power, hadexcellent optics, was aberration-free, was 74 mm in diameter, and had acenter of thickness of 1.7 mm. During the cooling steps, a small surfaceprobe thermistor was positioned against the outside of the gasket wallto monitor the reaction. The results are summarized below.

Elapsed Gasket Wall Time From Dose Temperature Dose (min) (F.) 5 flashesto back surface and 0 Not recorded 4 flashes to front surface 1 Notrecorded 2 78.4 3 77.9 4 76.9 5 75.9 1 flash to back surface 0 Notrecorded 1 76.8 2 77.8 3 78 4 77.8 1 flash to front surface 0 Notrecorded 1 79.4 2 81.2 3 81.1 4 79.7 5 78.7 6 77.5 7 77.4 1 flash tofront surface and 0 Not recorded 1 flash to back surface 1 78.8 2 78.8 378.0 2 flashes to front surface and 0 Not recorded 2 flashes to backsurface 1 80.2 2 79.8 3 78.3 4 76.7 4.5 76.3Improved Ultraviolet Lens Curing Apparatus

FIG. 30 depicts a schematic view of an embodiment of an ultraviolet lenscuring apparatus 400. The apparatus preferably includes a first lightgenerator 402 and a second light generator 404 for generating anddirecting ultraviolet light towards lens cell 52. First light generator402 is preferably configured to direct ultraviolet light toward a firstmold member of the lens cell, and second light generator 404 ispreferably configured to direct ultraviolet light toward a second moldmember of the lens cell. The light generators 402 and 404 may be mediumpressure mercury lamps for continuously directing ultraviolet lighttowards the lens cell or may be strobe light sources for deliveringpulses of ultraviolet light to the lens cell. In an embodiment, thestrobe light source is a xenon source having a flash tube made ofquartz. In an alternate embodiment, the strobe light source is a xenonsource having a flash tube made from, for example, borosilicate.

The apparatus may include shutter system 950 (shown in FIG. 7) andprogrammable logic controller 952. The shutter system is preferablyoperable to block at least a portion of the ultraviolet light directedtoward at least one of the mold members. Programmable logic controller952 is preferably coupled to the shutter and adapted to activate theshutter system. The shutters are preferably adapted to extend to blockpassage of ultraviolet light toward the lens cell and are preferablyadapted to retract to allow passage of the ultraviolet light toward thelens cell.

Apparatus 400 preferably includes an air manifold 406 that maysubstantially surround irradiation chamber 407. Air distribution device94 is preferably disposed on the surface of the air manifold to directair toward the non-casting face of at least one of the mold members. Theirradiation chamber preferably communicates with air plenum 412, whichdirects “effluent air” away from the irradiation chamber. As describedherein, “effluent air” is taken to mean air that has contacted at leastone of the mold members to remove heat from the lens forming materialcontained within the mold cavity. The lens cell is preferably securedwithin a lens holder of lens drawer 410 prior to being inserted into theirradiation chamber. The lens drawer may be inserted within and removedfrom the irradiation chamber and is preferably adapted to form asubstantially airtight seal with the air manifold when inserted into theirradiation chamber.

Apparatus 400 preferably includes a first cooling assembly 414 and asecond cooling assembly 416 for reducing the temperature of the air (andpreferably cooling the air to a temperature below ambient temperature)before it is passed from air distribution device 94 to the lens cell.FIG. 32 depicts a cross-sectional view of the irradiation chamber andthe cooling assemblies. Irradiation chamber 408 is preferably enclosedwith substantially airtight seals to inhibit or prevent cooling air fromescaping from the chamber. In an embodiment, members 420 and 422 may bepositioned on the air distribution devices to form a substantiallyairtight seal. Member 420 is preferably disposed between light generator402 and the first mold member, and member 422 is preferably disposedbetween light generator 404 and the second mold member. Members 420 and422 may be plates and are preferably substantially transparent to theultraviolet light delivered from light generators 402 and 404,respectively. In an embodiment, members 402 and 404 are substantiallyclear borosilicate glass. In an alternate embodiment, members 402 and404 are light diffusers for diffusing the ultraviolet light directed tothe lens cell. The light diffusers are preferably made of borosilicateglass that has been sandblasted to “frost” the glass. In an alternateembodiment, member 402 and 404 may be made from quartz glass.

In an embodiment, cooling assemblies 414 and 416 are thermoelectriccooling systems. Cooling assembly 414 may be used to cool air directedtoward the first mold member, and cooling assembly 416 may be used tocool air directed toward the second mold member. The cooling assembliesare preferably sized to cool the air to a temperature between about 0°C. and about 20° C.

Cooling assembly 414 preferably includes a thermoelectric module 422 forcreating a temperature differential to allow the air to be cooled tobelow ambient temperature. An exemplary thermoelectric module is shownin FIG. 33. The thermoelectric module is preferably connected to a DCpower source 440. The thermoelectric module is preferably asemiconductor wafer and preferably includes a plurality of semiconductorpn-couples disposed between a pair of ceramic plates 448 and 450containing metallization 446. The pn-couples are preferably connectedthermally in parallel and electrically in series. The thermoelectricmodule may be a single-stage or cascade module. When the thermoelectricmodule is connected to the DC power source, a phenomenon (i.e., “thePeltier effect”) occurs whereby heat is absorbed on cold side 448 andheat is dissipated from hot side 450. It is to be understood that theflow of current may be reversed to cause side 448 to dissipate heatwhile side 450 absorbs heat.

The publication entitled “An Introduction to Thermoelectrics”, availablefrom Tellurex Corp. of Traverse City, Mich. discusses suchthermoelectric modules and is incorporated by reference as if fully setforth herein. The pamphlet entitled “A Thermoelectric Bible on How toKeep Cool”, available from Supercool Corp. of Minneapolis, Minn. alsodescribes a thermoelectric module and is incorporated by reference as iffully set forth herein.

In FIG. 31, the side of the thermoelectric module facing upwards is thehot side. Cooling assembly 414 preferably includes a heat sink 428coupled to the hot side to facilitate the dissipation of heat from thethermoelectric module. The heat sink may be directly coupled to the hotside or the heat sink may be indirectly coupled to the hot side via amember having a relatively high thermal conductivity. In FIG. 31, theheat sink is indirectly coupled to the hot side by conductive block 424.Insulation 426 preferably substantially surrounds the thermoelectricmodule and the conductive block. In an embodiment, a fan 434 is used todirect air across heat sink 428 to increase the rate of heat dissipationfrom the thermoelectric module. The heat sink preferably includes aplurality of fins which serve as a heat transfer surface.

The cold side of the thermoelectric module is preferably coupled to acold side heat sink 430 serving to absorb heat to cool the air directedtoward the lens cell. The cold side heat sink may be located within airconduit 453 and preferably contains a plurality of fins through whichthe air is passed to cool it.

Cooling assembly 416 preferably includes second thermoelectric module423, second conductive block 425, second hot side heat sink 429, andsecond fan 435, each of which may operate in the manner as describedabove for the elements included within cooling assembly 414. In analternate embodiment, cooling assemblies 414 and 416 may beindependently operable to allow air directed toward the first moldmember to have a different temperature than air directed toward thesecond mold member.

A first blower 432 is preferably configured to direct air through airconduit 453, which communicates with air distribution device 94 a.Second blower 433 is preferably configured to direct air through airconduit 454, which communicates with air distribution device 94 b. Asdescribed herein, a “blower” is taken to mean any device operable todrive a fluid such as air through a conduit. The first blower preferablydrives air that is distributed across the non-casting face of the firstmold member. The second blower preferably drives air that is distributedacross the non-casting face of the second mold member. Effluent air thathas contacted the non-casting face of at least one of the mold membersis preferably passed through air plenum 412 and to blowers 432 and 433for recycling to air distribution devices 94 a and 94b. Each of thethermoelectric modules is preferably sized to cool about 1-30 cubic feetper minute of heated effluent air to a temperature of about 0-20° C.

In an alternate embodiment, the cooling assemblies may be used to reducethe temperature of the recirculated air to ambient temperature or atemperature above ambient temperature. The cooling assemblies may beactivated when the cooling air exceeds a predetermined temperature levelabove ambient temperature.

The thermoelectric cooling system has been found to operate morequietly, efficiently, and reliably than some conventional coolingsystems. Recirculating the effluent air through the closed cooling looptends to reduce the heat duty on the cooling system, since the effluentair in air plenum 412 preferably has a temperature less than ambienttemperature.

In an embodiment, a control panel 418 is operable to manually orautomatically control operation of apparatus 400. The control panel mayinclude an electronic controller for automatic control of systemvariables and a digital display 415 indicating the temperature of thecooling air at various locations in the air conduits, irradiationchamber, and air plenum. The control panel is preferably adapted toreceive electronic signals from temperature sensors 460, 462, and 464.Cavities may also be formed in conductive blocks 424 and 425 to holdtemperature sensors placed therein. The blowers 432 and 433 may beactivated or deactivated and the cooling assemblies may be engaged ordisengaged by switches on the control panel or by a programmable logiccontroller. The flow rate of air passed across the mold members may beadjusted via the control panel, or the flow rate may be maintained at aconstant rate during operation of blowers 432 and 433.

A programmable logic controller 417 may be housed within the controlpanel. Controller 417 is preferably adapted to independently controloperation of the light generators 402 and 404 such that ultravioletlight is directed in a plurality of pulses toward at least one of themold members. The controller 417 is preferably programmable such that apredetermined time elapses between each of the pulses to optimize thecuring cycle. The controller 417 may be adapted to cause the strobes tofire at predetermined times through the curing cycle, therebycontrolling the rate of polymerization and exothermic heat generation ofthe lens forming composition. One programmable logic controller that hasbeen found to perform adequately is the Little Star Microcontrollercombined with a Relay Six relay board, both commercially available fromZ-World Engineering of Davis, Calif. The strobe firing sequence may bewritten in Dynamic C programming language. The Ultra 1800 WhiteLightning photographic strobes, commercially available from Paul C.Buff, Incorporated of Nashville, Tenn., have been found to performadequately.

It is to be understood that embodiments of apparatus 400 may be combinedwith the methods and apparatus of preferred embodiments described abovein previous sections.

Improved Lens Curing Apparatus Example

An 80 mm diameter glass 28 flattop bifocal mold with a distance radiusof curvature of −5.98 diopters and a +2.50 diopter bifocal add power wassprayed with a mixture of isopropyl alcohol and distilled water in equalparts and wiped dry with a lint free paper towel. The mold was assembledinto a silicone rubber gasket in combination with a cleaned convex moldpossessing a radius of curvature of +4.11 diopters. A raised lip presenton the inner circumference of the rubber gasket provided a spacing of4.2 mm between the two molds at the center point.

The mold/gasket assembly was positioned on a filling stage and the edgeof the gasket was peeled back to permit the cavity to be filled with14.4 grams of OMB-91 lens forming composition, commercially availablefrom the FastCast Corporation of Louisville, Ky. The edge of the gasketwas returned to its sealing relationship with the edges of the molds andexcess lens forming composition was vacuumed off the non-casting surfaceof the back mold with a suction device. The filled mold/gasket assemblywas transferred from the filling stage to a stage incorporated into alens drawer of a strobe curing chamber. The assembly was irradiated onboth its sides according to the exposure cycle shown in FIG. 34, whichwas controlled by a programmable logic controller. The power settings onthe strobes were adjusted to maximum power.

During the irradiation, the lens cell was continuously exposed tostreams of recirculated air directed by the blower and cooled by thethermoelectric cooling module shown in FIGS. 31 and 32. At the beginningof the cycle, the air temperature was 68 degrees F. and at the end ofthe cycle is was measured at 73 degrees F. The air temperature variedduring the rest of the cycle up to temperatures as high as 90 degreesF., primarily as a result of the heat added to the system from both thestrobe flash lamps and the exothermic heat generated by the lens formingcomposition. It is anticipated that the operating temperatures of theair could be reduced to well below ambient temperature and the curingcycle could be shortened by use of thermoelectric coolers having agreater capacity than those used in this experiment.

The casting cell was turned over in the chamber so that its convexsurface faced upwards and was dosed with 13 flashes to the convexsurface and 10 flashes to the concave surface. The casting cell wasremoved from the strobe chamber, the gasket was stripped from theassembly, and residual uncured material was wiped from the exposed edgeof the lens. The cell was returned to the chamber with its concave sidefacing up and was dosed with an additional 13 flashes to the concavesurface and 10 flashes to the convex surface.

The non-casting surfaces of both the front and the back molds wereplaced in contact with thermal transfer pads, commercially availablefrom the FastCast Corporation of Louisville, Ky., at temperatures ofapproximately 150 to 200 degrees F. as measured on top of the pad forten minutes. The assembly was removed from the thermal transfer pad andthe back mold was removed with a slight impact from an appropriatelysized wedge. The lens with the front mold attached was placed in acontainer of water at room temperature and the lens separated from thefront mold. The now finished lens was sprayed with a mixture ofisopropyl alcohol and water in equal parts and wiped dry. The finishedlens was 4.0 mm thick at the center and was 74 mm in diameter. The lensexhibited a focusing power of +1.98 −0.02 D with a bifocal additionpower of +2.54 D, provided good optical quality, and was non-yellow.

Improved Lens Curing Process

When casting an eyeglass lens with ultraviolet light, the gelationpattern of the lens forming composition may affect the resultant opticalquality of the lens. If there are localized discontinuities in the lightintensities received by the monomer contained in the casting cavityduring the early stages of the polymerization process, opticaldistortions may be seen in the finished product. Higher power lensesare, by definition, thicker in certain regions than relatively lowerpower lenses of the same diameter. The layers of a lens closest to themold faces of the casting cavity tend to receive a higher lightintensity than the deeper layers because the lens forming compositionabsorbs some of the incident light. This causes the onset ofpolymerization to be delayed in the deeper layers relative to the outerlayers, which may cause optical distortions in the finished product. Itis believed that concurrent with this differential curing rate, there isa difference in the rate of exothermic heat generation, specifically,the deeper regions will begin to generate heat after the outer regionsin the cavity have already cured and the effectiveness of the heatremoval may be impaired, contributing to optical waves and distortionsin the finished product. This phenomena is particularly observable inhigh powered positive lenses due to the magnification of such defects.

In an embodiment, the lens forming composition contained within thecasting cavity is exposed to relatively high intensity ultraviolet lightfor a time period sufficient to initialize the reaction. Irradiation isterminated before the polymerization of the lens forming compositionproceeds far enough to generate a substantial amount of heat. Thisinitial relatively high intensity dose preferably substantiallyuniformly gels the material within the casting cavity such that thedifference in the rate of reaction between the inner and outer layers ofthe lens being cured is reduced, thereby eliminating the waves anddistortions often encountered when using continuous low intensityirradiation to initialize the reaction, particularly with high dioptricpower positive lenses.

In an embodiment, the relatively high intensity dose of ultravioletlight is applied to the lens forming composition in the form of pulses.The pulses preferably have a duration of less than about 10 seconds,preferably less than about 5 seconds, and more preferably less thanabout 3 seconds. The pulses preferably have an intensity of at leastabout 10 milliwatts/cm², more preferably at least about 100milliwatts/cm², and more preferably still between about 150milliwatts/cm² and about 250 milliwatts/cm². It is preferred thatsubstantially all of the lens forming composition forms into a gel afterthe initial application of the relatively high intensity ultravioletlight. In an embodiment, no more than an insubstantial amount of heat isgenerated by exothermic reaction of the lens forming composition duringthe initial application of the relatively high intensity ultravioletlight.

Subsequent to this initial high intensity dose, a second irradiationstep is performed in which the material contained within the castingcell is preferably irradiated for a relatively longer time at arelatively lower intensity while cool fluid is directed at thenon-casting surface of at least one of the molds forming the cavity. Thecooling fluid preferably removes the exothermic heat generated by thepolymerization of the lens forming composition. If the intensity of theultraviolet light is too great during this second irradiation step, therate of heat generation will tend to be too rapid and the lens mayrelease prematurely from the casting face of the mold and/or crack.Similarly, should the rate of heat removal from the lens formingcomposition be too slow, the lens may release prematurely and/or crack.It is preferred that the mold/gasket assembly containing the lensforming composition be placed within the cooling environment as shortlyafter the initial dose of ultraviolet light as possible.

In an embodiment, the ultraviolet light applied to the lens formingcomposition during the second irradiation step is less about 350microwatts/cm², more preferably less than about 150 microwatts/cm², andmore preferably still between about 90 microwatts/cm² and about 100microwatts/cm². During the second irradiation step, the ultravioletlight may be applied to the lens forming composition continuouslypreferred or in pulses. A translucent high density polyethylene platemay be positioned between the ultraviolet light generator and at leastone of the mold members to reduce the intensity of the ultraviolet lightto within a preferred range.

In an embodiment, relatively high intensity ultraviolet light is appliedto the lens curing composition in a third irradiation step to post curethe lens subsequent to the second relatively low intensity irradiationstep. In the third irradiation step, pulses of ultraviolet light arepreferably directed toward the lens forming composition, although thecomposition may be continuously irradiated instead. The pulsespreferably have an intensity of at least about 10 milliwatts/cm², morepreferably at least about 100 milliwatts/cm², and more preferably stillbetween about 100 milliwatts/cm² and about 150 milliwatts/cm².

Each of the above-mentioned irradiation steps is preferably performed bydirecting the ultraviolet light through each of the first and secondmold members. The eyeglass lens is preferably cured in a total time ofless than 30 minutes and is preferably free of cracks, striations,distortions, haziness, and yellowness.

It is believed that the above-described methods enable the production ofwhole lenses in prescription ranges beyond those currently attainablewith continuous low intensity irradiation. The method can be practicedin the curing of relatively high or low power lenses with a reducedincidence of optical distortions in the finished lens as compared toconventional methods. It is to be understood that the above-describedmethods may be used independently or combined with the methods andapparatus of preferred embodiments described above in the previoussections.

Improved Curing Process Example

An 80 mm diameter glass progressive addition mold with a nominaldistance radius of curvature of −6.00 diopters and a +2.50 diopterbifocal add power was sprayed with a mixture of isopropyl alcohol anddistilled water in equal parts and wiped dry with a lint free papertowel. The progressive mold was lenticularized to provide an opticalzone 68 mm in diameter along the 180 degree meridian and 65 mm indiameter along the 90 degree meridian. The non-casting face of the moldwas mounted to a suction cup, which was attached to a spindle. Thespindle was placed on a spinning device provided in the FastCast UX-462FlashCure Unit, commercially available from the FastCast Corporation ofLouisville, Ky. A one inch diameter pool of liquid Primer was dispensedinto the center of the horizontally positioned glass mold from a softpolyethylene squeeze bottle equipped with a nozzle with an orificediameter of approximately 0.040 inches. The composition of the Primer isdiscussed in detail below (see Scratch Resistant Lens Formation ProcessExample).

The spin motor was engaged to rotate the mold at a speed ofapproximately 850 to 900 revolutions per minute, which caused the liquidmaterial to spread out over the face of the mold. Immediatelythereafter, a steady stream of an additional 1.5 to 2.0 grams of Primermaterial was dispensed onto the casting face of the spinning mold withthe nozzle tip positioned at a 45 degree angle approximately 12 mm fromthe mold face such that the stream was flowing with the direction ofrotation of the mold. The stream of Primer material was directed firstat the center of the mold face and then dispensed along the radius ofthe mold face in a direction from the center toward the edge of the moldface. The solvent present in the Primer was allowed to evaporate off for8 to 10 seconds while the mold was rotated. The rotation was stopped andthe Primer coat present on the mold was cured via two exposures to theultraviolet output from the medium pressure mercury vapor lamp containedin the UX-462 FlashCure unit, totaling approximately 300 mJ/cm².

The spin motor was again engaged and approximately 1.5 to 2.0 grams ofHC8-H Hard Coat (see description below), commercially available from theFastCast Corporation of Louisville, Ky. was dispensed onto the spinningmold in a similar fashion as the Primer coat. The solvent present in theHC8-H was allowed to evaporate off for 25 seconds while the mold wasrotated. The rotation was stopped and the HC8-H coat was cured in thesame manner as the Primer coat.

The mold was removed from the FlashCure unit and assembled into asilicone rubber gasket in combination with a cleaned convex moldpossessing a radius of curvature of +2.00 diopters. The raised lippresent on the inner circumference of the rubber gasket provided aspacing of 6.3 mm between the two molds at the center point. Themold/gasket assembly was positioned on a filling stage and the edge ofthe gasket was peeled back to permit the cavity to be filled with OMB-91lens forming composition, commercially available from the FastCastCorporation of Louisville, Ky. The edge of the gasket was returned toits sealing relationship with the edges of the molds and the excess lensforming composition was vacuumed off the non-casting surface of the backmold with a suction device. The filled mold/gasket assembly was placedon a stage in the UX-462 FlashCure unit and subjected to four exposuresof the ultraviolet output from the six inch medium pressure mercuryvapor lamp, totaling approximately 600 mJ/cm².

Immediately following this initial dose of high intensity ultravioletlight, the assembly was transferred to the FC-132 curing chamber wherethe casting cell was continuously exposed to streams of air having atemperature of 42 degrees F. while being irradiated with very lowintensity ultraviolet light for eight minutes. The light intensitymeasured approximately 90 microwatts/cm² from above plus approximately95 microwatts/cm² from below, according to the plus lens lightdistribution pattern called for by the manufacturer. The lamp racks aretypically configured to deliver ultraviolet light having an intensity ofabout 300 microwatt/cm² for the standard fifteen minute curing cycle.The reduction in ultraviolet light intensity was accomplished byinserting a translucent high density polyethylene plate into the lightdistribution filter plate slot along with the plus lens lightdistribution plate. A translucent high density polyethylene plate waspositioned between the front mold member and one light distributionplate and between the back mold member and the other light distributionplate.

The assembly was subsequently returned to the UX-462 FlashCure unit andthe non-casting surface of the back mold was exposed to four doses ofhigh intensity UV light totaling approximately 1150 mJ/cm². The gasketwas stripped from the assembly and residual uncured material wiped fromthe exposed edge of the lens. An oxygen barrier strip (polyethylene) waswrapped around the edge of the lens and the mold was exposed to two moredoses of high intensity UV light totaling 575 mJ/cm² to the non-castingsurface of the front mold followed by eight more flashes to thenon-casting surface of the back mold totaling 2300 mJ/cm².

The non-casting surface of the back mold was placed in contact with athermal transfer pad, commercially available from the FastCastCorporation of Louisville, Ky., at a temperature of approximately 150 to200 degrees F. for thirteen minutes. The assembly was removed from thethermal transfer pad and the back mold was removed with a slight impactfrom an appropriately sized wedge. The front mold with the lens attachedthereto was placed in a container of room temperature water and the lensseparated from the front mold. The now-finished lens was sprayed with amixture of isopropyl alcohol and water in equal parts and wiped dry. Thelens read +3.98 D with an addition power of +2.50, was clear,non-yellow, and exhibited good optics.

Improved Scratch Resistant Lens Formation Process

The “in-mold” method involves forming a scratch resistant coating overan eyeglass lens by placing the liquid coating in a mold andsubsequently curing it. The in-mold method is advantageous to“out-of-mold” methods since the in-mold method exhibits less occurrencesof coating defects manifested as irregularities on the anterior surfaceof the coating. Using the in-mold method produces a scratch resistantcoating that replicates the topography and smoothness of the moldcasting face. However, a problem encountered when using conventionalin-mold scratch resistant coatings is that minute “pinholes” often formin the coating. It is believed that the pinholes are caused by eithercontaminants on the mold, airborne particles falling on the coatingbefore it is cured, or bubbles formed during the application of thecoating which burst afterwards. The formation of such pinholes isespecially prevalent when using a flat-top bifocal mold, such as the onedepicted in FIG. 35. As illustrated, the segment line 454 of a bifocalsegment 452 below the main surface 456 of the mold reduces thesmoothness of the casting face. When a coating is spin-coated over themold face, this indentation becomes an obstacle to the even flow of thecasting face. The pinhole defects are mainly a problem in tinted lensesbecause the dye used to tint a lens can penetrate through the pinholes,resulting in a tiny speck of dye visible in the lens.

According to an embodiment of the invention, a first coatingcomposition, i.e., a polymerizable “primer” material is passed through afilter and then placed within a mold member having a casting face and anon-casting face. The first coating composition preferably contains aphotoinitiator to make it curable upon exposure to ultraviolet light.The mold member may then be spun so that the first composition becomesdistributed over the casting face. The mold member is preferably rotatedabout a substantially vertical axis at a speed between about 750 andabout 1000 revolutions per minute. Further, a dispensing device may beused to direct an additional amount of the first composition onto thecasting face while the mold member is spinning. The dispensing devicepreferably moves from the center of the mold member to an edge of themold member so that the additional amount is directed along a radius ofthe mold member. Ultraviolet light is preferably directed at the moldmember to cure at least a portion of the first composition.

A second coating composition may then be placed upon the firstcomposition in the mold member. The second coating is also preferablycurable when exposed to ultraviolet light because it contains aphotoinitiator. The mold member is again spun to distribute the secondcoating composition over the cured portion of the first coatingcomposition. The mold member may also be spun simultaneously whileadding the second composition to the mold member. Ultraviolet light isthen preferably directed at the mold member to simultaneously cure atleast a portion of the second coating composition and form a transparentcombination coat having both coating compositions. The combination coatis preferably a substantially scratch-resistant coating. The mold membermay then be assembled with a second mold member by positioning a gasketbetween the members to seal them. Therefore, a mold having a cavityshared by the original two mold members is formed. An edge of the gasketmay be displaced to insert a lens-forming composition into the cavity.The combination coat and the lens-forming material preferably adherewell to each other. This lens-forming composition preferably comprises aphotoinitiator and is preferably cured using ultraviolet light. Airwhich preferably has a temperature below ambient temperature may bedirected toward a non-casting face of the second mold member to cool thelens-forming composition while it is being cured.

The primer coat preferably comprises a mixture of high viscositymonomers, a low viscosity, low flashpoint organic solvent, and asuitable photoinitiator system. The solvent may make up about more than80% of the mixture, preferably about 93% to 96%. This mixture preferablyhas low viscosity and preferably covers any surface irregularity duringthe spin application, for example the segment line of a flat-top bifocalmold. The low flashpoint solvent preferably evaporates off relativelyquickly, leaving a thin layer of high viscosity monomer, containingphotoinitiator, which coats the casting face of the mold. The curedprimer coat is preferably soft to allow it to adhere well to the glassmold face. Since the primer coat is soft, it may not possess scratchresistant characteristics. However, applying a high scratch resistancehard coating (i.e., the second coating composition) to the primer coatpreferably results in a scratch resistant combination coat. The hardcoat preferably contains a solvent which evaporates when the mold memberis rotated to distribute the hard coating over the primer coat.

In general, the ideal primer material preferably possesses the followingcharacteristics: exhibits chemical stability at normal storageconditions, e.g. at room temperature and in the absence of ultravioletlight; flows well on an irregular surface, especially over a flat-topbifocal segment; when cured with a specified ultra-violet dose, leaves acrack-free coating, with a high double bond conversion (approximatelygreater than 80%); maintains adhesion with the mold face through thelens forming curing cycle, especially the segment part of the flat-topbifocal mold; and is chemically compatible with the hard coat which issubsequently applied on top of it, e.g. forms an optically clearcombination coat. Even though pinhole defects may be present in eitherthe primer coat or the hard coat, it is highly unlikely that defects inone coat would coincide with defects of another coat. Each coatpreferably covers the holes of the other coat, resulting in lesspinholes in the combination coat. Thus, the finished in-mold coated lensmay be tinted using dye without problems created by pinholes. It is alsopreferably free of cracks, yellowness, haziness, and distortions.

In an embodiment, the gasket between the first mold member and thesecond mold member may be removed after a portion of the lens-formingmaterial has been cured. The removal of the gasket preferably exposes anedge of the lens. An oxygen barrier having a photoinitiator may beplaced around the exposed edge of the lens, wherein the oxygen barrierphotoinitiator is preferably near an uncured portion of the lens-formingcomposition. Additional ultraviolet rays may then be directed towardsthe lens to cause at least a portion of the oxygen barrierphotoinitiator to initiate reaction of the lens-forming material. Theoxygen barrier preferably prevents oxygen from contacting at least aportion of the lens forming composition during exposure of the lens tothe ultraviolet rays.

According to one embodiment, a substantially solid conductive heatsource is applied to one of the mold members. Heat may be conductivelytransferred from the heat source to a face of the mold member. Further,the heat may be conductively transferred through the mold member to theface of the lens.

Scratch Resistant Lens Formation Process Example

A first coating composition, hereinafter referred to as “Primer”, wasprepared by mixing the following components by weight:

-   93.87% acetone;-   3.43% SR-399 (dipentaerythritol pentaacrylate), available from    Sartomer;-   2.14% CN-104 (epoxy acrylate), available from Sartomer;-   0.28% Irgacure 184 (1-hydroxycyclohexylphenylketone), available from    Ciba-Geigy; and-   0.28% Darocur 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one)    available from Ciba-Geigy.

A second coating composition, hereinafter referred to as “HC8-H” wasprepared by mixing the following components by weight:

-   84.69% 1-methoxy 2-propanol;-   9.45% SR-399 (dipentaerythritol pentaacrylate), available from    Sartomer;-   4.32% SR601 (ethoxylated bisphenol A diacrylate), available from    Sartomer; and-   1.54% Irgacure 184 (1-hydroxycyclohexyl-phenyl ketone), available    from Ciba-Geigy.    Each of these coating compositions was prepared by first dissolving    the monomers into the solvent, then adding the photoinitiators,    mixing well, and finally passing the composition through a one    micron filter prior to use.

An 80 mm diameter glass 28 mm flattop mold with a distance radius ofcurvature of −6.00 diopters and a +2.00 diopter bifocal add power weresprayed with a mixture of isopropyl alcohol and distilled water in equalparts. The flattop mold was wiped dry with a lint free paper towel. Thenon-casting face of the mold was mounted to a suction cup, which wasattached to a spindle. The spindle was placed on the spinning deviceprovided in the FastCast UX-462 FlashCure Unit, commercially availablefrom the FastCast Corporation of Louisville, Ky.

A one inch diameter pool of liquid Primer was dispensed into the centerof the horizontally positioned glass mold. The Primer was dispensed froma soft polyethylene squeeze bottle equipped with a nozzle having anorifice diameter of approximately 0.040 inches. A spin motor of thespinning device was engaged to rotate the mold at a speed ofapproximately 850 to 900 revolutions per minute, causing the liquidPrimer to spread out over the face of the mold. Immediately thereafter,a steady stream of an additional 1.5 to 2.0 grams of Primer material wasdispensed onto the casting face of the spinning mold. The stream ofPrimer material was directed onto the casting face with the nozzle tippositioned at a 45 degree angle approximately 12 mm from the mold face.This positioning of the nozzle tip made the stream to flow with thedirection of rotation of the mold. The stream of Primer material wasdirected first at the center of the mold face and then dispensed alongthe radius of the mold face in a direction from the center toward theedge of the mold face.

The solvent present in the Primer was allowed to evaporate off for 8 to10 seconds during rotation of the mold. The rotation was stopped and thePrimer coat which remained on the mold was cured via two exposures tothe ultraviolet output from the medium pressure mercury vapor lampcontained in the UX-462 FlashCure unit, totaling approximately 300mJ/cm². All light intensity/dosage measurements cited herein were takenwith an International Light IL-1400 Radiometer equipped with an XLR-340BDetector Head, both commercially available from International Light,Inc. of Newburyport, Mass.

Upon exposure to the ultraviolet light, the spin motor was again engagedand approximately 1.5 to 2.0 grams of HC8-H Hard Coat, commerciallyavailable from the FastCast Corporation of Louisville, Ky. was dispensedonto the spinning mold in a similar fashion as the Primer coat. Thesolvent present in the HC8-H was allowed to evaporate off for 25 secondswhile the mold was spinning. The rotation was stopped, and the HC8-Hcoat was cured in the same manner as the Primer coat.

The mold was removed from the FlashCure unit and assembled into asilicone rubber gasket in combination with a cleaned convex moldpossessing a radius of curvature of +7.50 diopters. The raised lippresent on the inner circumference of the rubber gasket provided aspacing of 1.8 mm between the two molds at the center point. At thispoint, the mold/gasket assembly was positioned on a filling stage andthe edge of the gasket was peeled back to permit the cavity to be filledwith OMB-91 lens forming composition, commercially available from theFastCast Corporation of Louisville, Ky. The edge of the gasket wasreturned to its sealing relationship with the edges of the molds and theexcess lens forming composition was vacuumed off the non-casting surfaceof the back mold with a suction device.

The filled mold/gasket assembly was transferred from the filling stageto an FC-132 curing chamber, commercially available from the FastCastCorporation of Louisville, Ky. While in the chamber, the assembly wascontinuously irradiated from both sides for a period of 15 minutes atapproximately 300 microwatts/cm² from above and at approximately 350microwatts/cm² from below, according to the minus lens lightdistribution pattern called for by the manufacturer. During theirradiation, the casting cell was continuously exposed to streams of airhaving a temperature of 42° F.

The mold/gasket assembly was subsequently returned to the UX-462FlashCure unit. The non-casting surface of the back mold was exposed tofour doses of high intensity UV light totaling approximately 1150mJ/cm². The gasket was stripped from the assembly and residual uncuredmaterial was wiped from the exposed edge of the lens. An oxygen barrierstrip (polyethylene) was wrapped around the edge of the lens. Themold/gasket assembly was exposed to two more doses of high intensity UVlight, wherein 575 mJ/cm² total was directed to the non-casting surfaceof the front mold. Subsequently, eight more flashes of the UV light weredirected to the non-casting surface of the back mold, totaling 2300mJ/cm².

The non-casting surface of the back mold was placed in contact with athermal transfer pad, commercially available from the FastCastCorporation of Louisville, Ky., at a temperature of approximately 150 to200° F. for thirteen minutes. The mold/gasket assembly was removed fromthe thermal transfer pad, and the back mold was removed with a slightimpact from an appropriately sized wedge. The front mold with the lensattached thereto was placed in a container of room temperature water.While within the water, the lens became separated from the front mold.The now-finished lens was sprayed with a mixture of isopropyl alcoholand water in equal parts and wiped dry.

The lens was positioned in a holder and placed into a heated dye pot for5 minutes. The dye pot contained a solution of BPI Black, commerciallyavailable from Brain Power, Inc. of Miami, Fla., and distilled water ata temperature of approximately 190 degrees F. The lens was removed fromthe dye pot, rinsed with tap water, and wiped dry. The lens exhibited atotal visible light absorbance of approximately 80%. When inspected forcosmetic defects on a light table, no pinhole defects were observed.Further, the tint which had been absorbed by the back surface of thelens was found to be smooth and even.

Non-Polymerizable Scratch Resistant Coating Process Example

A non-polymerizable coating composition, hereinafter referred to as“Precoat”, was prepared by mixing the following materials by weight:99.80% acetone; and 0.20% BYK-300, a slip agent commercially availablefrom BykChemie.

An 80 mm diameter glass 28 mm flattop mold with a distance radius ofcurvature of −6.00 diopters and a +2.00 diopter bifocal add power wassprayed with a mixture of isopropyl alcohol and distilled water in equalparts. The mold was subsequently wiped dry with a lint free paper towel.The non-casting face of the mold was mounted to a suction cup, which wasattached to a spindle. The spindle was placed on the spinning deviceprovided in the FastCast UX-462 FlashCure Unit, commercially availablefrom the FastCast Corporation of Louisville, Ky.

A spin motor of the spinning device was engaged to rotate the mold at aspeed of approximately 850 to 900 revolutions per minute. A steadystream of approximately 2.0 to 3.0 grams of Precoat material wasdispensed onto the casting face of the spinning mold with the nozzle tippositioned at a 45 degree angle approximately 12 mm from the mold face,thereby causing the stream to flow with the direction of rotation of themold. The stream of Precoat material was directed first at the center ofthe mold face. The stream was then dispensed along the radius of themold face in a direction from the center toward the edge of the moldface. The intended purpose of the Precoat was to improve the wettingcharacteristics of the glass mold so that the HC8-H material would flowover it more evenly.

The solvent present in the Precoat evaporated off the spinning moldalmost instantly, and approximately 1.5 to 2.0 grams of HC8-H Hard Coatwas dispensed onto the casting face of the spinning mold. The HC8-H HardCoat was directed onto the casting face along the radius of the moldface in a direction from the center toward the edge. The nozzle tip waspositioned at a 45 degree angle approximately 12 mm from the mold facesuch that the stream was flowing with the direction of rotation of themold. The solvent present in the HC8-H was allowed to evaporate off for25 seconds while the mold was spinning. The rotation was stopped, andthe HC8-H coat was cured via two exposures to the ultraviolet outputfrom the medium pressure mercury vapor lamp contained in the UX-462FlashCure unit, totaling approximately 300 mJ/cm².

The mold was removed from the FlashCure unit and assembled into asilicone rubber gasket in combination with a cleaned convex moldpossessing a radius of curvature of +7.50 diopters. The raised lippresent on the inner circumference of the rubber gasket provided aspacing of 1.8 mm between the two molds at the center point. Themold/gasket assembly was positioned on a filling stage, and the edge ofthe gasket was peeled back to permit the cavity to be filled with OMB-91lens forming composition, commercially available from the FastCastCorporation of Louisville, Ky. The edge of the gasket was returned toits sealing relationship with the edges of the molds. The excess lensforming composition was vacuumed from the non-casting surface of theback mold with a suction device. The filled mold/gasket assembly wastransferred from the filling stage to an FC-132 curing chamber,commercially available from the FastCast Corporation of Louisville, Ky.The assembly was continuously irradiated from both sides for a period of15 minutes at approximately 300 microwatts/cm² from above andapproximately 350 microwatts/cm² from below, according to the minus lenslight distribution pattern called for by the manufacturer. During theirradiation, the casting cell was continuously exposed to streams of airhaving a temperature of 42° F.

The assembly was subsequently returned to the UX-462 FlashCure unit. Thenon-casting surface of the back mold was exposed to four doses of highintensity UV light, totaling approximately 1150 mJ/cm². The gasket wasstripped from the assembly, and residual uncured material was wiped fromthe exposed edge of the lens. An oxygen barrier strip (i.e.,polyethylene) was wrapped around the edge of the lens and the cell wasexposed to two more doses of high intensity UV light, wherein 575 mJ/cm²total were directed to the non-casting surface of the front mold. Eightmore flashes of high intensity UV light followed. The eight flashesexposed the non-casting surface of the back mold to a total of 2300mJ/cm².

The non-casting surface of the back mold was placed in contact with athermal transfer pad at a temperature of approximately 150 to 200° F.for thirteen minutes. The assembly was removed from the thermal transferpad, and the back mold was removed with a slight impact from anappropriately sized wedge. The front mold with the lens attached theretowas placed in a container of room temperature water in order to causethe lens to be separated from the front mold. The now-finished lens wassprayed with a mixture of isopropyl alcohol and water in equal parts andwiped dry.

The lens was positioned in a holder and placed into a heated dye pot for5 minutes. The dye pot contained a solution of BPI Black, commerciallyavailable from Brain Power, Inc. of Miami, Fla., and distilled water ata temperature of approximately 190° F. The lens was removed from the dyepot, rinsed with tap water and wiped dry. The lens exhibited a totalvisible light absorbance of approximately 80%. When inspected forcosmetic defects on a light table, several pinhole tint defects wereobserved. They appeared to be in the range of 0.2 mm to 0.05 mm indiameter. However, the tint which had been absorbed by the back surfaceof the lens was found to be smooth and even.

Ultraviolet Initiated Polymerization of a Lens Forming CompositionContaining Ultraviolet Absorbing Materials

Materials (hereinafter referred to as “ultraviolet absorbing compounds”)that absorb various degrees of ultraviolet light may be used in aneyeglass lens to inhibit ultraviolet light from being transmittedthrough the eyeglass lens. Such an eyeglass lens advantageously inhibitsultraviolet light from being transmitted to the eye of a user wearingthe lens. Thus eyeglass lenses containing ultraviolet absorbingcompounds may function to protect the eyes of a person from damagingultraviolet light. Photochromic pigments are one type of ultravioletabsorbing compounds. Photochromic inorganic lenses which contain silverhalide particles or cuprous halide particles suspended throughout thebody of the lens are well known and have been commercially available fordecades. Such inorganic lenses, however, suffer the disadvantage ofbeing relatively heavy and less comfortable to the wearer when comparedto organic lenses. Consequently, the majority of the eyeglass lensesproduced today are formed from organic materials rather than inorganicmaterials. Accordingly, photochromic plastic eyeglass lenses have beenthe subject of considerable attention in recent years.

Efforts to provide a plastic eyeglass lens which demonstratesphotochromic performance have primarily centered around permeatingand/or covering the surface(s) of an already formed lens withphotochromic pigments. This general technique may be accomplished by anumber of specific methods. For example, (a) the lens may be soaked in aheated bath which contains photochromic pigments, (b) photochromicpigments may be transferred into the surface of a plastic lens via asolvent assisted transfer process, or (c) a coating containingphotochromic pigments may be applied to the surface of a lens. A problemwith such methods is that the lens often might not absorb enough of thephotochromic pigments at low temperatures, resulting in an eyeglass lenswhich does not exhibit acceptable photochromic performance.Unfortunately, increasing the temperature used during absorption of thephotochromic pigments is not a solution to this problem since at hightemperatures degradation of the polymer contained within the lens mayoccur.

Attempts have also been made to incorporate photochromic pigments intothe liquid monomer from which plastic lenses are thermally polymerized.See U.S. Pat. No. 4,913,544 to Rickwood et al., wherein it is disclosedthat triethyleneglycol dimethacrylate monomer was combined with 0.2% byweight of various spiro-oxazine compounds and 0.1% benzoyl peroxide andsubsequently thermally polymerized to form non-prescription eyeglasslenses. Generally, efforts to incorporate photochromic pigments into theliquid monomer from which the lenses are polymerized have beenunsuccessful. It is believed that the organic peroxide catalystsutilized to initiate the thermal polymerization reaction tend to damagethe photochromic pigments, impairing their photochromic response.

Curing of an eyeglass lens using ultraviolet light to initiate thepolymerization of a lens forming composition generally requires that thecomposition exhibit a high degree of ultraviolet transmissibility sothat the activating radiation can penetrate to the deeper regions of thelens cavity. Otherwise the resulting cast lens may possess opticalaberrations and distortions. The cast lens may also contain layers ofcured material in the regions closest to the transparent mold faces,sandwiching inner layers which are either incompletely cured, gelled,barely gelled, or even liquid. Often, when even small amounts ofultraviolet absorbing compounds of the types well known in the art areadded to a normally UV curable lens forming composition, substantiallythe entire amount of lens forming composition contained within the lenscavity may remain liquid in the presence of activating radiation.

Photochromic pigments which have utility for photochromic eyeglasslenses absorb ultraviolet light strongly and change from an unactivatedstate to an activated state when exposed to light. The presence ofphotochromic pigments, as well as other ultraviolet absorbing compoundswithin a lens forming composition, generally does not permit enoughactivating radiation to penetrate into the depths of the lens cavitysufficient to cause ultraviolet photoinitiators to break down andinitiate polymerization of the lens forming composition. Thus, it isdifficult to cure a lens forming composition containing ultravioletabsorbing compounds using ultraviolet light. It is therefore desirableto provide a method for using ultraviolet light to initiatepolymerization of an eyeglass lens forming monomer which containsultraviolet absorbing compounds, in spite of the high ultravioletabsorption characteristics of the ultraviolet absorbing compounds.Examples of such ultraviolet absorbing compounds other than photochromicpigments are fixed dyes and colorless additives.

In an embodiment of the present invention, an ophthalmic eyeglass lensmay be made from a lens forming composition comprising a monomer, anultraviolet absorbing compound, an ultraviolet photoinitiator, and aco-initiator. Herein, an “ophthalmic eyeglass lens” is taken to mean anyplastic eyeglass lens, including a prescription lens, a non-prescriptionlens, a sunglass lens, and a bifocal lens. The lens forming composition,in liquid form, is preferably placed in a mold cavity defined by a firstmold member and a second mold member. It is believed that ultravioletlight which is directed toward the mold members to activate thephotoinitiator causes the photoinitiator to form a polymer chainradical. The polymer chain radical preferably reacts with theco-initiator more readily than with the monomer. The co-initiator mayreact with a fragment or an active species of either the photoinitiatoror the polymer chain radical to produce a monomer initiating species inthe regions of the lens cavity where the level of ultraviolet light iseither relatively low or not present.

The co-initiator is preferably activated only in the presence of thephotoinitiator. Further, without the co-initiator, the photoinitiatormay exclusively be activated near the surface of the lens formingcomposition but not within the middle portion of the composition.Therefore, using a suitable photoinitiator combined with a co-initiatorpermits polymerization of the lens forming composition to proceedthrough the depths of the lens cavity. A cured, clear, aberration freelens is preferably formed in less than about 30 minutes, more preferablyin less than about 10 minutes. Herein, a “clear lens” is taken to mean alens that transmits visible light without scattering so that objectsbeyond the lens are seen clearly. Herein, “aberration” is taken to meanthe failure of a lens to produce point-to-point correspondence betweenan object and its image. The lens, when exposed to ultraviolet lightpreferably inhibits at least a portion of the ultraviolet light frombeing transmitted through the lens that is preferably formed. A lensthat permits no ultraviolet light from passing through the lens (atleast with respect to certain UV wavelengths) is more preferred.

In an embodiment, the lens forming composition which contains anultraviolet absorbing compound may be cured with ultraviolet lightutilizing the UVEXS curing apparatus previously described herein anddepicted in FIG. 10. In another embodiment, the lens forming compositionmay be cured with ultraviolet light supplied from the FC-104 curingchamber which is depicted in FIGS. 14 and 15. Alternately, the lensforming composition may be cured by exposing the composition toultraviolet light multiple times using both the UVEXS and the FC-104.Preferably, all ultraviolet light directed toward the mold members is ata wavelength of 400 nm or below. The above-mentioned embodiments whichdescribe various methods for forming eyeglass lenses may also beutilized to form the eyeglass lens hereof.

The identity of the major polymerizable components of the lens formingcomposition tends to affect the optimal curing process. It isanticipated that the identity of the ultraviolet absorbing compoundpresent in the monomer or blend of monomers may affect the optimalphotoinitiator/co-initiator system used as well as the optimal curingprocess used to initiate polymerization. Also, varying the identities orthe proportions of the monomer(s) in the lens forming composition mayrequire adjustments to various production process variables including,but not limited to, exposure times, exposure intensities, cooling timesand temperatures, ultraviolet and thermal postcure procedures and thelike. For example, compositions comprising relatively slow reactingmonomers, such as bisphenol A bis allyl carbonate or hexanedioldimethacrylate, or compositions comprising relatively higher proportionsof such monomers may require either longer exposure times, higherintensities, or both. It is postulated that increasing the amount ofeither fast reacting monomer or the initiator levels present in a systemwill require reduced exposure times, more rigidly controlled lightdoses, and more efficient exothermic heat removal.

Preferably, the monomers selected as components of the lens formingcomposition are capable of dissolving the ultraviolet absorbingcompounds added to them. Herein, “dissolving” is taken to mean beingsubstantially homogeneously mixed with”. For example, monomers may beselected from a group including polyol (allyl carbonate) monomers,multi-functional acrylate monomers, and multi-functional methacrylicmonomers for use in an ultraviolet absorbing lens forming composition.

In an embodiment, the following mixture of monomers, hereinafterreferred to as PRO-629, may be blended together before addition of othercomponents required to make the lens forming composition. This blend ofmonomers is preferably used as the basis for a lens forming compositionto which ultraviolet absorbing compounds are added.

32% Tripropyleneglycol diacrylate (SR-306) 21% Tetraethyleneglycoldiacrylate (SR-268) 20% Trimethylolpropane triacrylate (SR-351) 17%Bisphenol A bis allyl carbonate (HiRi) 10% Hexanediol dimethacrylate(SR-239)

The acrylic and methacrylic monomers listed above are commerciallyavailable from Sartomer Company in Exton, Pa. The bisphenol A bis allylcarbonate is commercially available from PPG in Pittsburgh, Pa. Thehexanediol dimethacrylate is hereinafter referred to as HDDMA.

A polymerization inhibitor may be added to the monomer mixture atrelatively low levels to inhibit polymerization of the monomer atinappropriate times (e.g., during storage). Preferably about 0 to 50 ppmof monomethylether hydroquinone (MEHQ) are added to the monomer mixture.It is also preferred that the acidity of the monomer mixture be as lowas possible. Preferably less than about 100 ppm residual acrylic acidexists in the mixture. It is also preferred that the water content ofthe monomer mixture be relatively low, preferably less than about 0.15%.

Ultraviolet photoinitiators which have utility in the present inventionmay include: 1-hydroxycyclohexylphenyl ketone commercially availablefrom Ciba Additives under the trade name of Irgacure 184; mixtures ofbis(2,6-dimethoxybenzoyl)-(2,4,4-trimethyl pentyl)phosphine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one commercially available fromCiba Additives under the trade name of Irgacure 1700; mixtures ofbis(2,6-dimethoxybenzoyl)-(2,4,4 trimethyl pentyl)phosphine oxide and1-hydroxycyclohexylphenyl ketone commercially available from CibaAdditives under the trade names of Irgacure 1800 and Irgacure 1850;2,2-dimethoxy-2-phenyl acetophenone commercially available from CibaAdditives under the trade name of Irgacure 651;2-hydroxy-2-methyl-1-phenyl-propan-1-one commercially available fromCiba Additives under the trade names of Darocur 1173; mixtures of2,4,6-trimethylbenzoyldiphenylphoshine oxide and2-hydroxy-2-methyl-1-phenyl-propan-1-one commercially available fromCiba Additives under the trade name of Darocur 4265;2,2-diethoxyacetophenone (DEAP) commercially available from FirstChemical Corporation of Pascagoula, Miss., benzil dimethyl ketalcommercially available from Sartomer Company under the trade name ofKB-1; alpha hydroxy ketone commercially available from Sartomer companyunder the trade name of Esacure KIP100F; 2-methyl thioxanthone (MTX),2-chloro thioxanthone (CTX), thioxanthone (TX), and xanthone, allcommercially available from Aldrich Chemical; 2-isopropyl thioxanthone(ITX) commercially available from Aceto Chemical in Flushing, N.Y.;mixtures of triaryl sulfonium hexafluoroantimonate and propylenecarbonate commercially available from Sartomer Company under the tradenames of SarCat CD 1010, SarCat 1011, and SarCat KI85; diaryl iodoniumhexafluoroantimonate commercially available from Sartomer Company underthe trade name of SarCat CD-1012; mixtures of benzophenone and1-hydroxycyclohexylphenyl ketone commercially available from CibaAdditives under the trade name of Irgacure 500;2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanonecommercially available from Ciba Additives under the trade name ofIrgacure 369; 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one commercially available from Ciba Additives under the tradename of Irgacure 907;bis(η5-2,4-cyclopentadien-1yl)-bis-[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium commercially available from Ciba Additives under the trade nameof Irgacure 784 DC; mixtures of 2,4,6-trimethyl benzophenone and4-methylbenzophenone commercially available from Sartomer Company underthe trade name of EsaCure TZT; and benzoyl peroxide and methyl benzoylformate both available from Aldrich Chemical in Milwaukee, Wis.

A preferred ultraviolet photoinitiator is bis (2,6dimethoxybenzoyl)-(2,4,4-trimethyl pentyl)phosphine oxide, commerciallyavailable from Ciba Additives in Tarrytown, N.Y. under the trade name ofCGI-819. The amount of CGI-819 present in a lens forming compositioncontaining photochromic compounds preferably ranges from about 30 ppm byweight to about 2000 ppm by weight.

Co-initiators which may have utility in the present invention includereactive amine co-initiators commercially available from SartomerCompany under the trade names of CN-381, CN-383, CN-384, and CN-386,where these co-initiators are monoacrylic amines, diacrylic amines, ormixtures thereof. Other co-initiators include N,N-dimethyldiethanolamine(N,NMDEA), triethanolamine (TEA), ethyl-4-dimethylamino benzoate(E-4-DMAB), ethyl-2-dimethylamino benzoate (E-2-DMAB), all commerciallyavailable from Aldrich Chemicals. Co-initiators which may also be usedinclude n-butoxyethyl-4-dimethyl amino benzoate, P-dimethyl aminobenzaldehyde. Other co-initiators include N,N-dimethyl-para-toluidine,octyl-para-(dimethylamino) benzoate commercially available from TheFirst Chemical Group of Pascagoula, Miss.

Preferably, the co-initiator is N-methyldiethanolamine (NMDEA)commercially available from Aldrich Chemical in Milwaukee, Wis., CN-384commercially available from Sartomer Company, or CN-386 alsocommercially available from Sartomer Company. The quantity of NMDEApresent in a lens forming composition containing photochromic pigmentsis preferably between about 1 ppm by weight and 7% by weight and morepreferably between about 0.3% and 2% by weight. Further, certain fixedpigments which may be added to the lens forming composition to create abackground color within the lens (i.e., to tint the lens), may alsofunction as co-initiators. Examples of such fixed pigments includeThermoplast Blue P, Oil Soluble Blue II, Thermoplast Red 454,Thermoplast Yellow 104, Zapon Brown 286, Zapon Brown 287, allcommercially available from BASF Corporation in Holland, Mich.

Ultraviolet absorbing compounds which may be added to a normallyultraviolet transmissible lens forming composition include 2-(2Hbenzotriazole-2-yl)4-(1,1,3,3 tetramethyl butyl) phenol and2-hydroxy-4-methoxybenzophenone, both commercially available fromAldrich Chemical as well as mixtures of2-[4-((2-hydroxy-3-dodecyloxypropyl)-oxy]2-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylpheyl-1,3,5-triazinecommercially available from Ciba Additives under the trade name ofTinuvin 400, mixtures of poly (oxy-1,2-ethanediyl),a-(3-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropyl)-w-hydroxyand poly (oxy-1,2-ethanediyl),a-(3-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropyl)-w-(3-(3-(2H-benzotriazol-2-yl)-5-1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropoxy)commercially available from Ciba Additives under the trade name ofTinuvin 1130. Other UV absorbers may include Tinuvin 328, Tinuvin 900,2(2 hydroxy-5-methyl phenyl) benzotriazole, ethyl-2-cyano 3,3 diphenylacrylate, and phenyl salicylate.

While any number of families of photochromic pigments may beincorporated into the blend of monomers, either individually or incombination, spiropyrans, spironaphthoxazines, spiropyridobenzoxazines,spirobenzoxazines, naphthopyrans, benzopyrans, spirooxazines,spironaphthopyrans, indolinospironaphthoxazines,indolinospironaphthopyrans, diarylnaphthopyrans, and organometallicmaterials, such as phenylmercury compounds are of particular interest. Aphenylmercury compound available from Marks Polarized Corporation inHauppauge, N.Y. under the trade name of A241 may be an appropriateorganometallic material. The quantity of photochromic pigments presentin the lens forming composition is preferably sufficient to provideobservable photochromic effect. The amount of photochromic pigmentspresent in the lens forming composition may widely range from about 1ppm by weight to 5% by weight. In preferred compositions thephotochromic pigments are present in ranges from about 30 ppm to 2000ppm. In the more preferred compositions the photochromic pigments arepresent in ranges from about 150 ppm to 1000 ppm. The concentration maybe adjusted depending upon the thickness of the lens being produced toobtain optimal visible light absorption characteristics.

In an embodiment, hindered amine light stabilizers may be added to thelens forming composition. It is believed that these materials act toreduce the rate of degradation of the cured polymer caused by exposureto ultraviolet light by deactivating harmful polymer radicals. Thesecompounds may be effective in terminating oxygen and carbon freeradicals, and thus interfering with the different stages ofauto-oxidation and photo-degradation. A useful hindered amine lightstabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacatecommercially available from Ciba Additives under the trade name ofTinuvin 292. Hindered phenolic anti-oxidants and thermal stabilizers mayalso be added to a lens forming composition. The hindered phenoliccompounds hereof include thiodiethylenebis-(3,5,-di-tert-butyl-4-hydroxy)hydrocinnamate commercially availablefrom Ciba Additives under the trade name of Irganox 1035 and octadecyl3,5-bis(1,1-dimethylethyl)-4-hydroxybenzene-propanoate commerciallyavailable from Ciba Additives under the trade name of Irganox 1076.

Preferably, more than one monomer and more than one initiator are usedin a lens forming composition to ensure that the initial polymerizationof the lens forming composition with ultraviolet light does not occurover too short a period of time. The use of such a lens formingcomposition may allow greater control over the gel formation, resultingin better control of the optical quality of the lens. Further, greatercontrol over the rate of exothermic heat generation may be achieved.Thus, cracking of the lens and premature release of the lens from themold which are typically caused by the release of heat may be prevented.An example of a poor initiator system was observed when CGI-819 was usedalone as a photoinitiator in combination with the PRO-629 monomer blendto which ultraviolet absorbing compounds had been added. When such aninitiator system was used, a fast rate of reaction occurred near thesurface of the lens cavity while a very slow rate of reaction occurredin the deeper regions of the cavity. The resultant lens exhibitedunwanted waves and distortions.

In another example, a small amount of a co-initiator, i.e., NMDEA wasadded to the above lens forming composition. During the curing process,two separate waves of heat were generated when the composition wasirradiated continuously at about 600 microwatts/cm². One possibleexplanation of this phenomena is that the first wave resulted fromreaction of the NMDEA and the second wave resulted from the reaction ofthe unconsumed portion of the CGI-819. Another possible explanation isthat the rate of reaction was faster in the top portion than in thebottom portion of the lens forming composition since ultraviolet lightwas separately directed toward both the bottom and the top mold members.A third wave of heat generation may also occur if the rate of reactionat the middle portion of the lens forming composition is different fromthe rates at the bottom and top portions. Unfortunately, the resultinglens possessed waves and distortions. It is postulated, however, that asthe amounts of both CGI-819 and NMDEA are increased, the two waves ofexothermic heat will move closer together in time, causing the opticalquality of the lens to improve, the hardness of the lens to increase,and the rate of heat generation to be slow enough to prevent crackingand premature release of the lens from the mold.

It is anticipated that the optimal amounts of the lens formingcomposition components is where the total amount of both initiators areminimized subject to the constraint of complete polymerization andproduction of a rigid, aberration free lens. The relative proportions ofthe photoinitiator to the co-initiator may be optimized byexperimentation. For example, an ultraviolet absorptive lens formingcomposition that includes a photoinitiator with no co-initiator may becured. If waves and distortions are observed in the resulting lens, aco-initiator may then be added to the lens forming composition byincreasing amounts until a lens having the best optical properties isformed. It is anticipated that excess co-initiator in the lens formingcomposition should be avoided to inhibit problems of too rapidpolymerization, yellowing of the lens, and migration of residual,unreacted co-initiator to the surface of the finished lens.

The following charts may be used as a guide in the selection of anappropriate photoinitiator/co-initiator system for various UV absorbtivelens forming compositions.

Photoinitiator Guide Lens Forming Composition Type UV Absorbtive UVAbsorbtive UV Absorbtive Photoiniator Yellowness Odor Shelf LifePhotochromic Fixed Pigments Colorless CGI 819 Moderate Low Good GoodGood Good Irgacure 184 Low Low Good Good Good Good Irgacure 651 High LowPoor Less Preferred Good Less Preferred Irgacure 1700 High Low Fair GoodGood Less Preferred Irgacure 1800 Moderate Low Good Good Good LessPreferred Irgacure 1850 Moderate Low Good Good Good Good Darocur 1173High Low Good Good Good Less Preferred Darocur 4265 High Moderate FairGood Good Less Preferred DEAP High Strong Poor Less Preferred LessPreferred Less Preferred KB-1 High Strong Poor Less Preferred LessPreferred Less Preferred EsaCure KIP100F High Strong Poor Less PreferredLess Preferred Less Preferred Irgacure 369 High Moderate Poor LessPreferred Good Less Preferred Irgacure 500 High Strong Poor LessPreferred Less Preferred Less Preferred Irgacure 784 DC High Low PoorLess Preferred Less Preferred Less Preferred Irgacure 907 High StrongPoor Less Preferred Less Preferred Less Preferred Benzoyl peroxideModerate Low Poor Less Preferred Less Preferred Less Preferred Methylbenzoyl formate Moderate Low Fair Less Preferred Less Preferred LessPreferred EsaCure TZT High Low Poor Less Preferred Less Preferred LessPreferred ITX High Low Poor Less Preferred Good Good MTX High Low PoorLess Preferred Good Good CTX High Low Poor Less Preferred Less PreferredLess Preferred TX High Low Poor Less Preferred Less Preferred LessPreferred Xanthone High Low Poor Less Preferred Less Preferred LessPreferred CD-1010 Low Low Poor Good Less Preferred Less PreferredCD-1011 Low Low Poor Good Less Preferred Less Preferred CD1012 Low LowPoor Good Good Good Yellowness High, Moderate, Low Odor Strong,Moderate, Low Shelf life Good, Fair, Poor Lens Forming Composition TypeGood, Less Preferred Co-initiator Guide Lens Forming Composition Type UVAbsorbtive UV Absorbtive UV Absorbtive Co-initator Photochromic FixedPigments Colorless CN-383 Good CN-384 Good Good Good CN-386 Good GoodGood NMDEA Good Good Good N,NMDEA Less Preferred Less Preferred TEA LessPreferred Less Preferred E-4-DMAB Good Less Preferred Less PreferredE-2-DMAB Less Preferred Less Preferred Lens Forming CompositionType Good, Less Preferred

As mentioned above, exothermic reactions occur during the curing processof the lens forming composition. The thicker portions of the lensforming composition may generate more heat than the thinner portions ofthe composition as a result of the exothermic reactions taking place. Itis believed that the speed of reaction in the thicker sections is slowerthan in the thinner sections. Thus, in a positive lens a “donut effect”may occur in which the relatively thin outer portion of the lens formingcomposition reaches its fully cured state before the relatively thickinner portion of the lens forming composition. Conversely, in a negativelens the relatively thin inner portion of the lens forming compositionmay reach its fully cured state before the relatively thick outerportion of the lens forming composition.

Accordingly, it is preferred that a greater amount of ultraviolet lightis applied to the thicker sections of the composition than to thethinner sections. FIG. 36 depicts one embodiment in which a pair of moldmembers 500 are held together by a gasket 502 such that members 500define a cavity to make a positive lens. A filter 506 may be placeddirectly adjacent to at least one of the mold members 500. Filter 506may further be disposed between an ultraviolet light source (not shown)and the mold member. Alternately, filters may be placed adjacent to bothmold members (not shown). In one embodiment, as shown in FIG. 36, thethickness of the filter preferably varies so that a thinner section ofthe filter corresponds to an adjacent thicker section of the mold cavityand a thicker section of the filter corresponds to an adjacent thinnersection of the mold cavity. In other words, the thickness of the filtermay be varied according to the varying thickness of the lens formingcomposition disposed within the mold cavity. The filter is preferably ahazy filter that may be formed by a variety of means. The filter may bepolymerized from a hazy material or any combination of materials whichcreate haze. More specifically, the filter may be a “lens” (i.e., apiece of plastic shaped like a lens) made by adding an incompatiblechemical to a typical lens forming composition. For example, a bisphenolcompound may be added to a lens forming composition and polymerized,resulting in a cloudy filter in the shape of a lens that separates lightinto numerous (e.g., millions) of fragments. The filter may be injectionmolded from polyethylene or any suitable thermoplastic.

A purpose of the filter is to simultaneously diffuse light and providedifferential light distribution between the thin and thick sections ofthe mold cavity. See U.S. Pat. No. 5,415,816 for a discussion of theimportance of differential light distribution with respect to theultraviolet light initiated polymerization of eyeglass lenses. See U.S.Pat. No. 4,728,469 for a discussion of the importance of light diffusionwith respect to the ultraviolet initiated polymerization of eyeglasslenses. The filter is preferably translucent to ultraviolet light. Whena hazy filter is used, the ultraviolet light may be broken up into arelatively large number of fragments. It is believed that the amount oflight attenuation created by such a filter is proportional to thethickness of the filter. The diffusing characteristics of the filtertends to impact the occurrence of optical aberrations and distortions inthe finished lens.

In general, when curing a minus (negative) lens which is thin in thecenter and thick on the edge, it is preferable to use a filter which isthick in the center and thin at the edge adjacent to the mold members.When curing a plus (positive) lens which is thick in the center and thinon the edge, it is preferable to use a filter which is thin in thecenter and thick at the edge adjacent to the mold members. The locationof the filter is preferably chosen to be near the mold cavity so thatthe differential light distribution of the filter tends to be maximized.Thus, the ultraviolet light intensity directed toward the thick and thinregions of the mold cavity may be controlled more readily than if thefilter is further away from the mold members.

A flat-top bifocal mold, such as the one depicted in FIG. 35 reflectslight in different regions with different light intensities.Particularly, the segment, line 454 of the bifocal segment 452 reflectslight more than other areas of the mold, increasing the amount ofultraviolet light that the lens forming composition is exposed to in theregion near segment line 454. It is believed that this region of thelens forming composition will gel more rapidly state than other portionsof the lens forming composition. Thus, when using a flat-top bifocalmold to form a lens, it is desirable to diffuse ultraviolet light beforeit reaches the segment line of the mold, and thereby reduce the amountof light that is reflected at the segment line. In an embodiment inwhich a flat-top bifocal mold is being utilized, the use of a hazyfilter as described above is preferred.

In one embodiment, after the lens forming composition has been placed inthe mold cavity, it may be pre-cooled 3 to 7 minutes before beingexposed to ultraviolet light. Thus, the lens forming composition may becooled to below ambient temperature prior to polymerization of the lensforming composition. Advantageously, the heat released by the reactionwithin the composition may be balanced by the coolness of thecomposition so that the composition is not exposed to extreme amounts ofthermal radiation. Thus, exposing the lens forming composition to belowambient temperatures before the reaction is initiated may inhibitundesirable effects resulting from the exothermic nature of thereaction. For example, cooling the lens forming composition might helpprevent the loss of process control caused by variations in the rate ofreaction that result from temperature changes of the lens formingcomposition.

In an embodiment, the ultraviolet light is directed toward the moldmembers until at least a portion of the lens forming composition is agel. At this point, application of the ultraviolet light is preferablyterminated to inhibit the polymerization reaction from proceeding toorapidly, thereby inhibiting the rate of heat generation from increasingso rapidly that premature release of the lens from the mold cavityand/or cracking of the lens results. After termination of the light, thegasket holding the two mold members together is preferably removed toexpose the lens forming composition to air while the reaction is allowedto continue at a desired rate. The air may advantageously help cool thelens forming composition. In an embodiment, the lens forming compositionmay be exposed to ambient conditions for about 5 to 15 minutes,depending on the mass of the composition. Since the amount of heatreleased during reaction tends to be proportional to the mass of thecomposition, the more mass the composition has, the longer it may becooled. After cooling the composition, it may be exposed to ultravioletlight again if desired.

In an embodiment, the inner surface, i.e., the casting face, of thefront mold member may be coated with one or more hardcoat layers beforethe lens forming composition is placed within the mold cavity.Preferably, two hardcoat layers are used so that any imperfections, suchas pin holes in the first hardcoat layer, are covered by the secondhardcoat layer. The resulting double hardcoat layer is preferablyscratch resistant and protects the subsequently formed eyeglass lens towhich the double hardcoat layer adheres. In an embodiment, the castingface of the back mold member may be coated with a material that iscapable of being tinted with dye prior to filling the mold cavity withthe lens forming composition. This tintable coat preferably adheres tothe lens forming composition so that dyes may later be added to theresulting eyeglass lens for tinting the lens.

In an embodiment, dyes may be added to the lens forming composition. Itis believed that certain dyes may be used to attack and encapsulateambient oxygen so that the oxygen cannot react with free radicals formedduring the curing process. Also, dyes may be added to the composition toalter the color of an unactivated photochromic lens. For instance, ayellow color that sometimes results after a lens is formed may be“hidden” if a blue-red or blue-pink dye is present in the lens formingcomposition. The unactivated color of a photochromic lens may also beadjusted by the addition of non-photochromic pigments to the lensforming composition.

In an embodiment, the eyeglass lens that is formed may be coated with ahydrophobic layer, e.g. a hardcoat layer. The hydrophobic layerpreferably extends the life of the photochromic pigments near thesurfaces of the lens by preventing water and oxygen molecules fromdegrading the photochromic pigments.

In a preferred embodiment, both mold members are coated with a curedadhesion-promoting composition prior to placing the lens formingcomposition into the mold cavity. Providing the mold members with suchan adhesion-promoting composition is preferred to increase the adhesionbetween the casting surface of the mold and the lens formingcomposition. The adhesion-promoting composition thus reduces thepossibility of premature release of the lens from the mold. Further, itis believed that such a coating also provides an oxygen and moisturebarrier on the lens which serves to protect the photochromic pigmentsnear the surface of the lens from oxygen and moisture degradation. Yetfurther, the coating provides abrasion resistance, chemical resistance,and improved cosmetics to the finished lens.

An eyeglass lens formed using the lens forming composition of thepresent invention is not only applicable for use as a prescription lensand may be used for a non-prescription lens as well. Particularly, sucha lens may be used in sunglasses. Advantageously, photochromic sunglasslenses would remain light enough in color to allow a user to see throughthem clearly while at the same time prohibiting ultraviolet light frompassing through the lenses. In one embodiment, a background dye may beadded to the photochromic lens to make the lens appear to be a darkshade of color at all times like typical sunglasses.

Each of the embodiments described above may be combined or usedindividually.

Casting a Plastic Lens Containing Photochromic Material Process Example

A polymerizable mixture of PRO-629 (see above for a description of thecomponents of PRO-629), photochromic pigments, and an ultravioletphotoinitiator/co-initiator system was prepared according to thefollowing procedure. A photochromic stock solution was prepared bydissolving the following pigments into 484 grams of HDDMA.

Pigment grams % by wt. Dye #94 1.25 0.250% Dye #266 0.45 0.090%Variacrol Red PNO 2.66 0.532% Variacrol Yellow L 1.64 0.328% ReversacolCorn Yellow 3.58 0.716% Reversacol Berry Red 2.96 0.590% Reversacol SeaGreen 2.17 0.434% Reversacol Palatinate Purple 1.29 0.258% Total 16.03.200%

Dye #94 and Dye #266 are indolino spiropyrans commercially availablefrom Chroma Chemicals, Inc. in Dayton, Ohio. Variacrol Red PNO is aspironaphthoxazine material and Variacrol Yellow L is a naphthopyranmaterial, both commercially available from Great Lakes Chemical in WestLafayette, Ind. Reversacol Corn Yellow and Reversacol Berry Red arenaphthopyrans and Reversacol Sea Green and Reversacol Palatinate Purpleare spironaphthoxazine materials commercially available from KeystoneAnaline Corporation in Chicago, Ill.

The powdered pigments were weighed and placed in a beaker. The HDDMA wasadded to the powdered pigments, and the entire mixture was heated to atemperature in the range from about 50° C. to 60° C. and stirred for twohours. Subsequently, the photochromic stock solution was cooled to roomtemperature and then gravity fed through a four inch deep bed ofaluminum oxide basic in a one inch diameter column. Prior to passing thestock solution through the alumina, the alumina was washed with acetoneand dried with air. The remaining HDDMA was forced out of the aluminawith pressurized air. It is believed that this filtration step removesany degradation by-products of the photochromic pigments and/or anyimpurities present in the mixture. After the filtration step, the stocksolution was passed through a 1 micron filter to remove any aluminaparticles which may have passed out of the column with the stocksolution.

A photoinitiator stock solution containing an ultraviolet photoinitiatorcombined with an ultraviolet absorber was also prepared by mixing 2.56grams of CGI-819 and 0.2 grams of Tinuvin 400, an ultraviolet absorbercommercially available from Ciba Additives of Tarrytown, N.Y., with97.24 grams of PRO-629. The stock solution was stirred for two hours atroom temperature in the absence of light. The photoinitiator stocksolution was then filtered by passing it through a layer of alumina anda one micron filter. The stock solution was placed in an opaquepolyethylene container for storage.

A background dye stock solution was prepared by mixing 50 grams of a 422ppm solution of A241/HDDMA, 50 grams of a 592 ppm solution ofThermoplast Red 454/HDDMA, 50 grams of 490 ppm solution of Zapon Brown286/HDDMA, 50 grams of 450 ppm solution of Zapon Brown 287/HDDMA, 50grams of 1110 ppm solution of Oil Soluble Blue II/HDDMA, and 50 grams ofa 1110 ppm solution of Thermoplast Blue P/HDDMA, all with 700 grams ofPRO-629. The entire mixture was heated to a temperature ranging fromabout 50° C. to 60° C. and subsequently stirred for two hours.

A lens forming composition was prepared by adding 12.48 grams of theabove described photochromic stock solution, 10 grams of thephotoinitiator stock solution, 27 grams of the background dye stocksolution, and 7.3 grams of the NMDEA co-initiator to 943.22 grams ofPRO-629. The components of the lens forming composition were stirred atroom temperature for several minutes until well mixed. This compositionis hereafter referred to as PC #1. The PC#1 contained the followingamounts of components.

Component Amount Tripropyleneglycol diacrylate 31.16%Tetraethyleneglycol diacrylate 20.45% Trimethylolpropane triacrylate19.47% Bispenol A bis allyl carbonate 16.55% Hexanediol dimethacrylate11.56% Dye #94 31.20 ppm Dye #266 11.20 ppm Variacrol Red PNO 66.40 ppmVariacrol Yellow L 40.90 ppm Reversacol Corn Yellow 89.30 ppm ReversacolBerry Red 73.60 ppm Reversacol Sea Green 54.20 ppm Reversacol PalatinatePurple 32.20 ppm A241 0.57 ppm Thermoplast Red 454 0.80 ppm Zapon Brown286 0.66 ppm Zapon Brown 287 0.61 ppm Oil Soluble Blue II 1.50 ppmThermoplast Blue 1.50 ppm CGI-819 255.90 ppm NMDEA 0.73% Tinuvin 40020.00 ppm

An 80 mm diameter concave glass progressive addition mold having adistance radius of curvature of 6.00 diopters and a +1.75 diopterbifocal add power was sprayed with a mixture of isopropyl alcohol anddistilled water in equal parts and wiped dry with a lint free papertowel. The mold was then mounted with its casting face upward on thecenter of a stage. The mold was fixed securely to the stage using threeequidistant clip-style contact points to hold the periphery of the mold.The mold stage had a spindle attached to it which was adapted to connectto a spinning device of a FastCast UX-462 Flashcure Unit, commerciallyavailable from the FastCast Corporation of Louisville, Ky. The moldstage, with the mold affixed, was placed on the spinning device in theFlashCure unit. The mold was rotated at approximately 750 to 900revolutions per minute. A stream of isopropyl alcohol was directed atthe casting surface while the casting surface was simultaneously brushedwith a soft camel hair brush to clean the surface. After the cleaningstep, the mold surface was dried by directing a stream of reagent gradeacetone over the surface and allowing it to evaporate off, all whilecontinuing the rotation of the mold.

The rotation of the mold was then terminated and a one inch diameterpool of a liquid coating composition was dispensed into the center ofthe horizontally positioned glass mold from a soft polyethylene squeezebottle equipped with a nozzle having an orifice diameter ofapproximately 0.040 inches. The spin motor was engaged to rotate themold at a speed of approximately 750 to 900 revolutions per minute,causing the liquid material to spread out over the face of the mold.Immediately thereafter, a steady stream of an additional 1.5 to 2.0grams of the coating composition was dispensed onto the casting face ofthe spinning mold. The stream was moved from the center to the edge ofthe casting face with a nozzle tip positioned at a 45° angleapproximately 12 mm from the mold face. Thus, the stream was flowingwith the direction of rotation of the mold.

The solvent present in the coating composition was allowed to evaporatewhile rotating the mold for 10 to 15 seconds. The rotation was stopped,and then the coating composition on the mold was cured via totallingexposures of approximately 300 mJ/cm² of ultraviolet light. The lightwas provided from a medium pressure mercury vapor lamp contained in theUX-462 FlashCure unit. All light intensity/dosage measurements citedherein were taken with an International Light IL-1400 Radiometerequipped with an XLR-340B Detector Head, both commercially availablefrom International Light, Inc. of Newburyport, Mass. At this point, thespin motor was again engaged and approximately 1.5 to 2.0 grams ofadditional coating composition was dispensed onto the spinning mold. Thesolvent of the composition was allowed to evaporate, and the compositionwas cured in a similar fashion to the first layer of coatingcomposition.

The above described coating composition comprised the followingmaterials:

Material % by wt. Irgacure 184 0.91% Dye Absorption 0.80% StabilizerCN-104 2.00% SR-601 1.00% SR-399 8.60% Acetone 26.00%  Ethanol 7.00%1-Methoxypropanol 53.69% Irgacure 184 is a UV photoinitiator commercially available from CibaAdditives, Inc. CN-104 is an epoxy acrylate oligomer, SR-601 is anethoxylated bisphenol A diacrylate, and SR-399 is dipentaerythritolpentaacrylate, all available from Sartomer Company in Exton, Pa. Theacetone, the ethanol, and the 1-methoxypropanol were all reagent gradesolvents. The dye absorption accelerator improves the impact resistanceof the lens and is available from Crs di Claudio Crose in Milan, Italy.

An 80 mm diameter convex mold with radii of curvature of 6.80/7.80diopters was cleaned and coated using the same procedure described aboveexcept that no pooling of the coating composition occurred in the centerof the mold when the composition was dispensed thereto.

The concave and convex molds were then assembled together with asilicone rubber gasket. A raised lip on the inner circumference of therubber gasket provided a spacing of 2.8 mm between the two molds at thecenter point. At this point the mold/gasket assembly was positioned on afilling stage. The edge of the gasket was peeled back to permit thecavity to be filled with PC #1 lens forming composition. The edge of thegasket was returned to its sealing relationship with the edges of themolds, and the excess lens forming composition was vacuumed from thenon-casting surface of the back mold with a suction device. The filledmold/gasket assembly was then transferred from the filling stage to theUX-462 curing chamber. The assembly was placed with the back mold facingupward on a black stage configured to hold the mold/gasket assembly.

An ultraviolet light filter was then placed on top of the back mold. Thefilter was approximately 80 mm in diameter which is the same as the molddiameter. The filter also had a spherical configuration with a centerthickness of 6.7 mm and an edge thickness of 5.5 mm. The filter wastaken from a group of previously made filters. These filters were formedby using eyeglass lens casting molds and gaskets to create cavities thatwere thickest in the center (a plus spherical cavity) and cavities thatwere thinnest in the center (a minus spherical cavity). A toriccomponent was also incorporated with some of these cavities to formcompound cavities.

The filter cavities were filled with an ultraviolet light curablecomposition comprising by weight; 99.37% PRO-629, 0.35% K-Resin, 0.27%NMDEA, 121 ppm CGI-819, and 10 ppm Tinuvin 400. K-resin is astyrene-butadiene copolymer commercially available from PhillipsChemical Company. To form this composition, the K-resin was firstdissolved in toluene. An appropriate amount of the K-resin toluenesolution was added to the PRO-629, and then the toluene was evaporatedoff by heat and stirring. The NMDEA, CGI-19, and the Tinuvin 400 werethen added to the PRO-629/K-Resin solution. The compositions containedin the cavities were cured by exposure to ultraviolet radiation. Whenthe cured article was removed from the mold cavity, it exhibited a highdegree of haze caused by the incompatibility of the PRO-629 and theK-Resin. In the strictest sense of the word, it should be noted thatthese filters were not “lenses” because their function was not to focuslight but rather to scatter and diffuse light.

The mold/gasket assembly and the filter were then irradiated with fourconsecutive doses of ultraviolet light totaling approximately 1150mJ/cm², as previously measured at the plane of the mold cavity with nofilter or any other intervening media between the light source and theplane. The mold/gasket assembly was then turned over on the stage sothat the front mold was facing upward. The mold/gasket assembly wasfurther rotated 90 degrees around the paraxial axis from its originalposition. The light filter was then placed over the front mold. Theentire assembly was then exposed to two more doses of ultraviolet lighttotaling approximately 575 mJ/cm². The mold/gasket assembly was removedfrom the curing chamber. The gasket was removed from the molds, and theexposed edge of the lens was wiped to remove any residual liquid. Themolds with lens were then placed in a vertical orientation in a rack,and the non-casting faces of both the front and back molds were exposedto ambient room temperature air for a period of approximately tenminutes. At this point, the entire mold assembly was returned to theUX-462 chamber. Then, without the aforementioned light filter in place,the mold assembly was dosed with four exposures totaling 600 mJ/cm²directed toward the back mold and two exposures totaling 300 mJ/cm²directed toward the front mold.

Subsequent to these exposures, the junction of the back mold and thelens was scored with the edge of a brass spatula. The back mold was thenremoved from the lens by positioning an appropriate sized Delrin wedgebetween the front and back molds and applying a sharp impact to thewedge. The lens, along with the front mold to which it was attached, washeld under running tap water and simultaneously brushed with a softbrush to remove any flakes or particles of polymer from the edges andsurface of the lens. The front mold was then separated from the lens bybreaking the seal between the two with the point of a pin pressedagainst the junction of the front mold and the lens. The lens was thenplaced concave side upward on a lens stage of similar design to the moldstage, except that the peripheral clips were configured to secure asmaller diameter workpiece. The lens stage, with the lens affixed, waspositioned on the spinning device of the UX-462 unit and rotated atabout 750 to 900 revolutions per minute. A stream of isopropyl alcoholwas directed at the concave surface while simultaneously brushing thesurface with a soft, clean brush.

After brushing, a stream of isopropyl alcohol was directed at thesurface of the lens, and the rotation was continued for a period ofapproximately 30 seconds until the lens was dry. The lens was turnedover on the stage so that the convex surface of the lens faced upward.Then the cleaning procedure was repeated on the convex surface. With theconvex surface facing upward, the lens was dosed with four exposures ofultraviolet light totaling approximately 1150 mJ/cm². The lens was againturned over on the stage such that the concave surface was upward. Thelens was subjected to an additional two exposures totaling 300 mJ/cm².The lens was removed from the stage and placed in a convection oven at115° C. for five minutes. After annealing the lens, it was removed fromthe oven and allowed to cool to room temperature. At this point the lenswas ready for shaping by conventional means to fit into an eyeglassframe.

The resulting lens was approximately 72 mm in diameter. The lens had acenter thickness of 2.6 mm, a distance focusing power of −0.71-1.00diopters, and a bifocal addition strength of 1.74 diopters. The lensappeared to have a bleached color of tan. Also, the lens that was formedexhibited approximately 75% visible transmittance as measured with aHoya ULT-3000 meter. The lens was exposed to midday sunlight at atemperature of approximately 75° F. for 3 minutes. After being exposedto sunlight, the lens exhibited a grey color and a visible lighttransmittance of approximately 15%. The optics of the lens appeared tobe crisp, without aberrared areas in either the distance or the bifocalsegment regions. The same lens forming composition was cured to form apIano lens so that the lens could be scanned with a Hewlett PackardModel 8453 UV-Vis spectrophotometer. See FIG. 37 for a plot of %transmittance versus wavelength (nm), as exhibited by the plano lens inits lightened state (i.e., without sunlight exposure). The lensexhibited very little transmittance of light at wavelengths below about370 nm.

The eyeglass lens of this example was cured using ultraviolet light eventhough the lens forming composition included UV absorbing photochromicpigments. Since photochromic pigments tend to absorb UV light strongly,the ultraviolet light might not have penetrated to the depths of thelens forming composition. The lens forming composition, however,contained a co-initiator in conjunction with a photoinitiator to helppromote the curing of the entire lens forming composition. The presentexample thus demonstrates that a photochromic lens containing both aphotoinitiator and a co-initiator may be cured using ultraviolet lightto initiate polymerization of the lens forming composition.

Casting a Colorless Lens Containing UV Absorbers Example

According to a preferred embodiment, a polymerizable mixture of PRO-629(see above for a description of the components of PRO-629), colorlessultraviolet absorbing compounds, an ultraviolet stabilizer, backgrounddyes, and an ultraviolet photoinitiator/co-initiator package wasprepared according to the following procedure. Six separate stocksolutions were prepared. One stock solution contained thephotoinitiator, two stock solutions contained UV absorbing compounds,one stock solution contained co-initiators, one stock solution containeda UV stabilizer, and one stock solution contained a background dyepackage. Each of these stock solutions were treated by passing themthrough a one inch diameter column packed with approximately 30 grams ofalumina basic. It is believed that this step reduced the impurities andtrapped the acidic byproducts present in each of the additives to thePRO-629. The following is a detailed description of the preparation ofthe polymerizable mixture mentioned above.

About 500 grams of a photoinitiator stock solution was prepared bydissolving 2.5% by weight of bis(2,6-dimetoxybenzoyl)(2,4,4 trimethylphenyl) phosphine oxide (CGI-819 commercially available from CibaAdditives) in Pro-629. This mixture was passed through an alumina basiccolumn in the dark.

About 500 grams of the UV absorber stock solution was prepared bydissolving 2.5% by weight of 2(2H-benzotriazol-2-yl)-4-(1,1,3,3tetramethyl)phenol (98% purity) in PRO-629. This mixture was also passedthrough an alumina basic column.

About 500 grams of a co-initiator stock solution was prepared by mixing70% by weight of CN-384 (a reactive amine co-initiator commerciallyavailable from Sartomer Company) in Pro-629. This mixture was passedthrough an alumina basic column.

About 271 grams of a UV stabilizer stock solution was prepared by mixing5.55% by weight of Tinuvin 292 in PRO-629. This mixture was passedthrough an alumina basic column.

About 250 grams of a UV absorber stock solution was prepared by mixing5.0% Tinuvin 400 (i.e., a mixture of2-[4-((2-hydroxy-3-dodecyloxypropyl)-oxy]2-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylpheyl-1,3,5-triazine))by weight in PRO-629. This mixture was passed through an alumina basiccolumn.

About 1000 grams of a background dye stock solution was prepared bymixing about 50 grams of a 592 ppm solution of Thermoplast Red454/HDDMA, 50 grams of 490 ppm solution of Zapon Brown 286/HDDMA, 50grams of 450 ppm solution of Zapon Brown 287/HDDMA, 50 grams of 1110 ppmsolution of Oil Soluble Blue II/HDDMA, and 50 grams of a 1110 ppmsolution of Thermoplast Blue P/HDDMA, all with 750 grams of PRO-629. Theentire mixture was heated to a temperature between about 50° and 60° C.and stirred for two hours. This mixture was passed through an aluminabasic column.

About 250 grams of CN-386 (a reactive amine co-initiator commerciallyavailable from Sartomer Company) was passed through an alumina basiccolumn.

A lens forming composition was prepared by mixing 967.75 grams ofPro-629 with 12.84 grams of the 2.5% 2(2H-benzotriazol-2-yl)-4-(1,1,3,3tetramethyl)phenol UV absorber stock solution, 4.3 grams of the 70%CN-384 co-initiator stock solution, 8.16 grams of the 2.5% CGI-819photoinitiator stock solution, 0.53 grams of the CN-386, 1.54 grams ofthe Tinuvin 400 UV absorber stock solution, 0.92 grams of the Tinuvin292 UV stabilizer stock solution, and 4.0 grams of the background dyestock solution. The resulting lens forming composition contained thefollowing components:

Material % by weight PRO-629  99.10% 2(2H-benzotriazol-2-yl)-4-(1,1,3,3tetramethyl)phenol 321 ppm Tinuvin 400  77 ppm Tinuvin 292  51 ppmCN-384  0.3% CN-386  0.53% CGI-819 204 ppm Thermoplast Red  0.12 ppmZapon Brown 286  0.10 ppm Zapon Brown 287  0.10 ppm Oil Soluble Blue II 0.22 ppm Thermoplast Blue  0.22 ppm

An 80 mm diameter 28 flattop concave glass mold with a distance radiusof curvature of 2.85 diopters and a +3.00 diopter bifocal add power wassprayed with a mixture of isopropyl alcohol and distilled water in equalparts and wiped dry with a lint free paper towel. The mold was thenmounted with its casting face upward on a stage. The mold was fixedsecurely to the center of the stage using three equidistant clip-stylecontact points at the periphery of the mold. The mold stage had aspindle attached to it which was adapted to fit into the spinning deviceprovided in the FastCast UX-462 FlashCure Unit, commercially availablefrom the FastCast Corporation of Louisville, Ky. The mold stage, withthe mold affixed, was placed on the spinning means in the FlashCureunit. The mold was rotated at approximately 750 to 900 revolutions perminute. A stream of the isopropyl alcohol was directed at the castingsurface while the casting surface was simultaneously brushed with a softcamel hair brush to clean the surface. After the cleaning step, the moldsurface was dried by directing a stream of reagent grade acetone overthe surface and allowing it to evaporate off, all while continuing therotation of the mold.

The rotation of the mold was then terminated and one inch diameter poolof a liquid coating composition was dispensed into the center of thehorizontally positioned glass mold from a soft polyethylene squeezebottle equipped with a nozzle with an orifice diameter of approximately0.040 inches. The spin motor was engaged to begin to rotate the mold ata speed of approximately 750 to 900 revolutions per minute, causing theliquid material to be spread out over the face of the mold. Immediatelythereafter, a steady stream of an additional 1.5 to 2.0 grams of thecoating composition was dispensed onto the casting face of the spinningmold. The stream was moved from the center to the edge of the castingface with a nozzle tip positioned at a 45 degree angle, approximately 12mm from the mold face. Thus, the stream was flowing with the directionof rotation of the mold.

The solvent present in the coating composition was allowed to evaporateoff for 10 to 15 seconds while rotating. The rotation was stopped, andthen the coating composition present on the mold was cured via twoexposures to the ultraviolet output from the medium pressure mercuryvapor lamp contained in the UX-462 FlashCure unit, totalingapproximately 300 mJ/cm². All light intensity/dosage measurements citedherein were taken with an International Light IL-1400 Radiometerequipped with an XLR-340B Detector Head, both commercially availablefrom International Light, Inc. of Newburyport, Mass.

The above described coating composition comprised the followingmaterials:

Material % by wt. Irgacure 184  0.91% Dye Absorption  0.80% AcceleratorCN-104  2.00% SR-601  1.00% SR-399  8.60% Acetone 26.00% Ethanol  7.00%1-Methoxypropanol 53.69%Irgacure 184 is a UV photoinitiator commercially available from CibaAdditives, Inc. CN-104 is an epoxy acrylate oligomer, SR-601 is anethoxylated bisphenol A diacrylate, and SR-399 is dipentaerythritolpentaacrylate, all available from Sartomer Company in Exton, Pa. Theacetone, the ethanol, and the 1-methoxypropanol were all reagent gradesolvents. The dye absorption accelerator improves the impact resistanceof the lens and is available from Crs di Crose in Milan, Italy.

An 80 mm diameter convex mold with radii of curvature of 7.05 diopterswas cleaned and coated in the same fashion described above except thatno pooling of the coating composition occurred in the center of the moldwhen the composition was dispensed thereto.

Both the concave and convex molds were then provided with a curedadhesion-promoting coating composition. By providing such a coating, theadhesion between the casting surface of the glass mold and the lensforming composition was increased, thereby reducing the possibility ofpremature release of the lens from the mold. The coating furtherprovided abrasion resistance, chemical resistance, and improvedcosmetics to the finished lens.

The concave and convex molds were then assembled into a silicone rubbergasket. A raised lip present on the inner circumference of the rubbergasket provided a spacing of 1.7 mm between the two molds at the centerpoint. At this point the mold/gasket assembly was positioned on afilling stage. The edge of the gasket was peeled back to permit thecavity to be filled with the above described colorless lens formingcomposition containing the UV absorbing compounds. The edge of thegasket was returned to its sealing relationship with the edges of themolds, and the excess lens forming composition was vacuumed off thenon-casting surface of the back mold with a suction device. The filledmold/gasket assembly was then transferred from the filling stage to theUX-462 curing chamber and placed back mold upward on a black stageconfigured to hold the mold/gasket assembly.

An ultraviolet light filter was then placed on top of the back mold. Thefilter was approximately 80 mm in diameter which is the same as the molddiameter. It had a plano configuration with a thickness of 3.1 mm. Thisfilter transmitted approximately 30% of the incident ultraviolet lightfrom the source as measured using the IL1400 radiometer with a XRL-340Bdetector head. The filter was taken from a group of previously madefilters. The fabrication of these filters was discussed in the Casting APlastic Lens Containing Photochromic Material Example (see above).

The mold/gasket assembly in which the lens forming composition had beenplaced and which had been covered by the above described filter was thenirradiated with four consecutive doses of ultraviolet light totalingapproximately 600 mJ/cm², as measured using the IL-1400 Radiometerequipped with the XLR-340B detector. This measurement was taken at theplane of the mold cavity while no filter or any intervening media waspresent between the light source and the plane. The mold/gasket assemblywas then turned over on the stage so that the front mold was facingupward. The mold/gasket assembly was further rotated 90 degrees aroundthe paraxial axis from its original position. The light filter was thenreplaced over the front mold. The entire assembly was exposed to twomore doses of ultraviolet light totaling approximately 300 mJ/cm².

The mold/gasket assembly was then removed from the curing chamber, andthe gasket was removed from the assembly. The mold with lens was thenreturned to the UX-462 curing chamber such that the back mold was facingupward. An opaque rubber disc, approximately 80 mm in diameter wasplaced over the back mold. This disc had the function of preventingultraviolet light from impinging on the major portion of the materialcontained within the cavity. With the disc in position, the cell wasexposed to two more exposures at 300 mJ/cm². This subsequent exposurewas used to cure the residual liquid around the edges of the lens,particularly around the junction between the front mold and the lens andto help seal the periphery. The mold assembly was removed from thecuring chamber and placed in a vertical orientation in a rack. Thenon-casting faces of both the front and back molds were then exposed toambient room temperature air for a period of approximately fifteenminutes. At this point, the entire mold assembly was returned to theUX-462 chamber and, without the aforementioned light filter or opaquedisc in place, was dosed with two exposures totaling 300 mJ/cm² directedtoward the back mold and two exposures totaling 300 mJ/cm² directedtoward the front mold.

Subsequent to these exposures, the junction of the back mold and thelens was scored with the edge of a brass spatula. The back mold was thenremoved from the lens by positioning an appropriate sized Delrin wedgebetween the front and back mold and applying a sharp impact to thewedge. The lens, with the front mold attached, was held under runningtap water and simultaneously brushed with a soft brush to remove anyflakes or particles of polymer from the edges and surface of the lens.The front mold was then separated from the lens by breaking the sealbetween the two with the point of a pin pressed against the junction ofthe front mold and the lens. The lens was then placed concave sideupward on a lens stage of similar design to the mold stage except thatthe peripheral clips were configured to secure a smaller diameterworkpiece. The lens stage, with the lens affixed, was positioned on thespinning device of the UX-462 unit and rotated at 750 to 900 revolutionsper minute. A stream of isopropyl alcohol was directed at the concavesurface while simultaneously brushing with a soft, clean brush.

After brushing, a stream of isopropyl alcohol was directed at thesurface of the lens, and the rotation was continued for a period ofapproximately 30 seconds until the lens was dry. The lens was turnedover on the stage so that the convex surface of the lens was upward.Then the cleaning procedure was repeated on the convex surface. With theconvex surface upward, the lens was dosed with four exposures ofultraviolet light totaling approximately 1150 mJ/cm². The lens wasturned over on the stage so that the concave surface faced upward. Thelens was subjected to an additional two exposures totaling 300 mJ/cm².The lens was removed from the stage and placed in a convection oven at115° C. for five minutes. The lens was then removed from the oven andallowed to cool to room temperature. At this point, the lens was readyfor shaping by conventional means to fit into an eyeglass frame.

The resulting lens was approximately 72 mm in diameter, had a centerthickness of 1.5 mm, a distance focusing power of −4.08 diopters, and abifocal addition strength of 3.00 diopters. The resultant lens was waterwhite. The optics of the lens were crisp, without aberrated areas ineither the distance or the bifocal segment regions. The same lensforming composition was cured to form a plano lens. The piano lens wasscanned with a Hewlett Packard Model 8453 UV-Vis spectrophotometer. SeeFIG. 38 for a plot of % transmittance versus wavelength (nm), asexhibited by the photochromic lens when exposed to sunlight. The lensexhibited virtually no transmittance of light at wavelengths below about370 nm. Also shown in FIG. 38 is the results of a similar scan made on aplano lens formed using the OMB-91 lens forming composition (see PulsedUltraviolet Light Application section above for components of OMB-91).The OMB-91 lens, which has no ultraviolet absorbing compounds, appearsto transmit light at wavelengths shorter than 370 nm, unlike thecolorless lens that contained ultraviolet absorbing compounds.

The eyeglass lens of this example was cured using ultraviolet light eventhough the lens forming composition included ultraviolet absorbingcompounds. Since ultraviolet absorbing compounds tend to absorb UV lightstrongly, the UV light might not have penetrated to the depths of thelens forming composition. The lens forming composition, however,contained a co-initiator in conjunction with a photoinitiator to helppromote the curing of the entire lens forming composition. The presentexample thus demonstrates that a lens containing ultraviolet absorbingcompounds may be cured using ultraviolet light to initiatepolymerization of a lens forming composition which contains aphotoinitiator/co-initiator system.

Casting a Colored Lens Containing UV Absorbers Example

According to a preferred embodiment, a polymerizable mixture of PRO-629(see above for a description of the components of PRO-629), fixedpigments, and an ultraviolet photoinitiator/co-initiator package wasprepared according to the following procedure. Nine separate stocksolutions were prepared. Seven of the stock solutions contained fixedpigments, one of the stock solutions contained a UV absorbing compound,and one of the stock solutions contained a photoinitiator. Each of thesestock solutions were treated by passing them through a one inch diametercolumn packed with approximately 30 grams of alumina basic. It isbelieved that this step reduces the impurities and traps the acidicbyproducts present in each of the additives to the PRO-629.

For each of the following fixed pigments, a stock solution was preparedby the following procedure. The pigments used were Thermoplast Red 454,Thermoplast Blue P, Oil Soluble Blue II, Zapon Green 936, Zapon Brown286, Zapon Brown 287, Thermoplast Yellow 284. One gram of each pigmentwas dissolved in 499 grams of HDDMA. Each mixture was heated to atemperature in the range from about 50° C. to 60° C. for approximatelytwo hours. This mixture was passed through an alumina basic column. Thealumina was then washed with 200 grams of HDDMA at a temperature of 50°C. to 60° C. followed by 300 grams of PRO-629 at a temperature of 50° C.to 60° C. This washing step ensured that any pigments trapped in thealumina were washed into the stock solution. This resulted in stocksolutions which contained a 0.1% concentration of each pigment in 29.97%PRO-629 and 69.93% HDDMA.

About 250 grams of the UV absorber stock solution was prepared bydissolving 5.0% Tinuvin 400 (a mixture of2-[4-((2-hydroxy-3-dodecyloxypropyl)-oxy]2-2hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and2-[4-((2-hydroxy-3-tridecyloxypropyl)-oxy]-2-hydroxyphenyl]-4,6-bis(2,4-dimethylpheyl-1,3,5-triazine)by weight in PRO-629. This mixture was passed through an alumina basiccolumn.

About 500 grams of the photoinitiator stock solution was prepared bydissolving 2.5% by weight of bis(2,6-dimetoxybenzoyl)(2,4,4 trimethylphenyl) phosphine oxide (CGI-819 commercially available from CibaAdditives) in Pro-629. This mixture was passed through an alumina basiccolumn in the dark.

A lens forming composition was prepared by mixing 685.3 grams of Pro-629with 10.48 grams of the 2.5% CGI-819 photoinitiator stock solution, 5.3grams of NMDEA (N-methyldiethanolamine is commercially available fromAldrich Chemicals), 0.6 grams of Tinuvin 400 UV absorber stock solution,7 grams of the Thermoplast Red stock solution, 58.3 grams of theThermoplast Blue stock solution, 55.5 of the Oil Soluble Blue II stocksolution, 29.2 grams of the Zapon Green 936 stock solution, 68.1 gramsof the Zapon Brown 286 stock solution, 38.9 grams of the Zapon Brown 287stock solution, and 41.3 grams of the Thermoplast Yellow 104 stocksolution. The resulting lens forming composition contained the followingcomponents:

Material % by weight Bisphenol A bis allyl carbonate  13.35%Tripropyleneglycol diacrylate  25.13% Tetraethyleneglycol diacrylate 16.49% Trimethylopropane triacrylate  15.71% Hexanediol dimethacrylate 28.75% Thermoplast Red  7.0 ppm Zapon Brown 286  68.1 ppm Zapon Brown287  38.9 ppm Oil Soluble Blue II  55.5 ppm Thermoplast Blue  58.3 ppmZapon Green 936  29.2 ppm Thermoplast Yellow 104  41.3 ppm NMDEA  0.53%CGI-819 262 ppm Tinuvin 400  30 ppm

An 80 mm diameter single vision concave glass mold with a distanceradius of curvature of 6.00 diopters was sprayed with a mixture ofisopropyl alcohol and distilled water in equal parts and wiped dry witha lint free paper towel. The mold was then mounted with its casting faceupward on the center of a stage. The mold was fixed securely to thestage with three equidistant clip-style contact points at the peripheryof the mold. This mold stage had a spindle attached to it which wassized to fit into a spinning device of a FastCast UX-462 FlashCure Unit,commercially available from the FastCast Corporation of Louisville, Ky.The mold stage, with the mold affixed, was placed on the spinning devicein the FlashCure unit. The mold was rotated at approximately 750 to 900revolutions per minute. A stream of the isopropyl alcohol was directedat the casting surface while the casting surface was simultaneouslybrushed with a soft camel hair brush. After the cleaning step, the moldsurface was dried by directing a stream of reagent grade acetone overthe surface and allowing it to evaporate off, all while continuing therotation of the mold.

The rotation of the mold was then terminated. A one inch diameter poolof a liquid coating composition was dispensed into the center of thehorizontally positioned glass mold from a soft polyethylene squeezebottle equipped with a nozzle with an orifice diameter of approximately0.040 inches. The spin motor was engaged to begin to rotate the mold ata speed of approximately 750 to 900 revolutions per minute, which causedthe liquid material to be spread out over the face of the mold.Immediately thereafter, a steady stream of an additional 1.5 to 2.0grams of the said coating composition was dispensed onto the castingface of the spinning mold. The stream was moved from the center to theedge of the casting face with a nozzle tip positioned at a 45° angleapproximately 12 mm from the mold face. Thus, the stream was flowingwith the direction of rotation of the mold.

The solvent present in the coating composition was allowed to evaporateoff for 10 to 15 seconds while rotating the mold. The rotation wasstopped, and then the coating composition present on the mold was curedvia two exposures to the ultraviolet output from the medium pressuremercury vapor lamp contained in the UX-462 FlashCure unit, totalingapproximately 300 mJ/cm². All light intensity/dosage measurements citedherein were taken with an International Light IL-1400 Radiometerequipped with an XLR-340B Detector-Head, both commercially availablefrom International Light, Inc. of Newburyport, Mass.

The above described coating composition comprised the followingmaterials:

Material % by wt. Irgacure 184  0.91% Dye Absorption  0.80% AcceleratorCN-104  2.00% SR-601  1.00% SR-399  8.60% Acetone 26.00% Ethanol  7.00%1-Methoxypropanol 53.69%Irgacure 184 is a UV photoinitiator commercially available from CibaAdditives, Inc. CN-104 is an epoxy acrylate oligomer, SR-601 is anethoxylated bisphenol A diacrylate, and SR-399 is dipentaerythritolpentaacrylate, all available from Sartomer Company in Exton, Pa. Theacetone, the ethanol, and the 1-methoxypropanol were all reagent gradesolvents. The dye absorption accelerator improves the impact resistanceof the lens and is available from Crs di Claudio Crose in Milan, Italy.

An 80 mm diameter convex mold with radii of curvature of 6.05 diopterswas cleaned and coated in the same fashion except that no pooling of thecoating composition occurred in the center of the mold when thecomposition was dispensed thereto.

The concave and convex molds were then coated with a curedadhesion-promoting coating composition. By providing such a coating, theadhesion between the casting surface of the glass mold and the curinglens forming composition was increased, thereby reducing the possibilityof premature release of the lens from the mold. The coating alsoprovided abrasion resistance, chemical resistance, and improvedcosmetics to the finished lens.

The concave and convex molds were then assembled together with anethylene vinyl acetate gasket. A raised lip on the inner circumferenceof the rubber gasket provided a spacing of 3.0 mm between the two moldsat the center point. At this point the mold/gasket assembly was fixturedon a filling stage. The edge of the gasket was peeled back to permit thecavity to be filled with the above described colorless lens formingcomposition which contained UV absorbing compounds. The edge of thegasket was returned to its sealing relationship with the edges of themolds, and the excess lens forming composition was vacuumed off thenon-casting surface of the back mold with a suction device. The filledmold/gasket assembly was transferred from the filling stage to theUX-462 curing chamber. The assembly was placed back mold upward on ablack stage configured to hold the mold/gasket assembly.

An ultraviolet light filter was then placed on top of the back mold. Thefilter was approximately 80 mm in diameter which is the same as the molddiameter. It had a plano configuration with a thickness of 3.1 mm. Thisfilter transmitted approximately 30% of the incident ultraviolet lightfrom the source as measured using the IL1400 radiometer with a XRL-340Bdetector head. The filter was taken from a group of previously madefilters. The fabrication of these filters was discussed in the Casting APlastic Lens Containing Photochromic Material Example.

The mold/gasket assembly, containing the lens forming composition wasthen irradiated with six consecutive doses of ultraviolet light totalingapproximately 1725 mJ/cm², as previously measured using the IL-1400Radiometer equipped with the XLR-340B detector at the plane of the moldcavity with no filter or any intervening media between the light sourceand the plane. The mold/gasket assembly was then turned over on thestage so that the front mold was facing upward. The entire assembly wasthen exposed to six more doses of ultraviolet light totalingapproximately 1725 mJ/cm². The mold/gasket assembly was removed from thecuring chamber. The gasket was removed from the molds, and the assemblywas placed in a vertical orientation in a rack such that the non-castingfaces of both the front and back molds were exposed to ambient roomtemperature air for a period of approximately ten minutes. At thispoint, the assembly was returned to the UX-462 chamber and was dosedwith four exposures totaling 600 mJ/cm² directed toward the back moldand four exposures totaling 600 mJ/cm² directed toward the front mold.

Subsequent to these exposures, the junction of the back mold and thelens was scored with the edge of a brass spatula. The back mold wasremoved from the lens by positioning an appropriate sized Delrin wedgebetween the front and back mold and applying a sharp impact to thewedge. The lens, with the front mold attached, was held under runningtap water and simultaneously brushed with a soft brush to remove anyflakes or particles of polymer from the edges and surface of the lens.The front mold was then separated from the lens by breaking the sealbetween the two with the point of a pin pressed against the junction ofthe front mold and the lens. The lens was then placed concave sideupward on a lens stage of similar design to the mold stage, except thatthe peripheral clips were configured to secure a smaller diameterworkpiece. The lens stage, with the lens affixed, was positioned on thespinning device of the UX-462 unit and rotated at 750 to 900 revolutionsper minute. A stream of isopropyl alcohol was directed at the concavesurface while simultaneously brushing with a soft, clean brush.

After brushing, a stream of isopropyl alcohol was directed at thesurface of the lens, and the rotation was continued for a period ofapproximately 30 seconds until the lens was dry. The lens was turnedover on the stage so that the convex surface of the lens faced upward.Then the cleaning procedure was repeated on the convex surface. With theconvex surface facing upward, the lens was dosed with four exposures ofultraviolet light totaling approximately 1150 mJ/cm². The lens wasturned over on the stage so that the concave surface was upward. Thelens was dosed with an additional two exposures totaling 300 mJ/cm². Thelens was removed from the stage and placed in a convection oven at 115°C. for five minutes. The lens was then removed from the oven and allowedto cool to room temperature. At this point the lens was ready forshaping by conventional means to fit into an eyeglass frame.

The resulting lens was approximately 74 mm in diameter, had a centerthickness of 2.7 mm, and a distance focusing power of +0.06 diopters.The resultant lens was dark green/greyish in color and could be used asa sunglass lens. The optics of the lens were crisp, without aberratedareas. The lens exhibited visible light transmission of approximately10%. When scanned with a Hewlett Packard Model UV-Vis spectrophotometer,the lens transmitted virtually no light at wavelengths less than 650 nm.

The sunglass lens of this example was cured using ultraviolet light eventhough the lens forming composition included ultraviolet absorbing fixedpigments. Since such fixed pigments tend to absorb UV light strongly,the UV light might not have penetrated to the depths of the lens formingcomposition. The lens forming composition, however, contained aco-initiator in conjunction with a photoinitiator to help promote thecuring of the entire lens forming composition. The present example thusdemonstrates that a sunglass lens containing ultraviolet absorbing fixedpigments may be cured using ultraviolet light to initiate polymerizationof a lens forming composition which contains aphotoinitiator/co-initiator system.

Further Improvements

Light Initiated Polymerization of a Lens Forming Composition ContainingLight Absorbing Materials

Curing of an eyeglass lens using activating light to initiate thepolymerization of a lens forming composition generally requires that thecomposition exhibit a high degree of activating light transmissibilityso that the activating light can penetrate to the deeper regions of thelens cavity. Otherwise the resulting cast lens may possess opticalaberrations and distortions. The cast lens may also contain layers ofcured material in the regions closest to the transparent mold faces,sandwiching inner layers which are either incompletely cured, gelled,barely gelled, or even liquid. Often, when even small amounts ofactivating light absorbing compounds have been added to a normallycurable lens forming composition, substantially the entire amount oflens forming composition contained within the lens cavity may remainliquid in the presence of activating light.

Photochromic pigments which have utility for photochromic eyeglasslenses typically absorb activating light strongly and change from aninactivated state to an activated state when exposed to activatinglight. The presence of photochromic pigments, as well as otheractivating light absorbing compounds within a lens forming composition,generally does not permit enough activating radiation to penetrate intothe depths of the lens cavity sufficient to cause photoinitiators tobreak down and initiate polymerization of the lens forming composition.Examples of such activating light absorbing compounds other thanphotochromic pigments are fixed dyes and colorless additives.

It is therefore difficult to cure a lens forming composition containingactivating light absorbing compounds using activating light. Onesolution to this problem involves the use of a co-initiator. By using aco-initiator, activating light may be used to initiate thepolymerization reaction. It is believed that activating light which isdirected toward the mold members may cause the photoinitiator to form apolymer chain radical. The polymer chain radical preferably reacts withthe co-initiator more readily than with the monomer. The co-initiatormay react with a fragment or an active species of either thephotoinitiator or the polymer chain radical to produce a monomerinitiating species in the regions of the lens cavity where the level ofactivating light is either relatively low or not present. It istherefore desirable to provide a method for polymerizing an eyeglasslens forming composition which contains light absorbing compounds byusing activating light having a wavelength which is not absorbed by thelight absorbing compounds, thus avoiding the need for a co-initiator.

In an embodiment of the present invention, an ophthalmic eyeglass lensmay be made from a lens forming composition comprising a monomer, alight (e.g., ultraviolet light) absorbing compound, and aphotoinitiator, by irradiation of the lens forming composition withactivating light. As used herein “activating light” means light that mayaffect a chemical change. Activating light may include ultravioletlight, visible light or infrared light. Generally any wavelength oflight capable of affecting a chemical change may be classified asactivating. Chemical changes may be manifested in a number of forms. Achemical change may include, but is not limited to, any chemicalreaction which causes a polymerization to take place. Preferably thechemical change causes the formation of a initiator species within thelens forming composition, the initiator species being capable ofinitiating a chemical polymerization reaction.

The lens forming composition, in liquid form, is preferably placed in amold cavity defined by a first mold member and a second mold member. Itis believed that activating light, when directed toward and through themold members to activate the photoinitiator, causes the photoinitiatorto form a polymer chain radical. The polymer chain radical may reactwith a fragment or an active species of either photoinitiator or thepolymer chain radical to produce a monomer initiating species in otherregions of the lens cavity.

The use of activating light of the appropriate wavelength preferablyprevents the lens from darkening during the curing process. Herein,“darkening” means becoming at least partially non-transparent to theincoming activating light such that the activating light may notsignificantly penetrate the lens forming composition. Photochromiccompounds may cause such darkening. Ultraviolet absorbing compoundspresent in the lens forming composition may prevent activating lighthaving a wavelength substantially below about 380 nm from penetratinginto the lens forming composition. When treated with activating lightcontaining light with wavelengths in the ultraviolet region, e.g. lightwith wavelengths below about 380 nm, the ultraviolet absorbing compoundsdarken, preventing further ultraviolet activating light from penetratingthe lens forming composition. The darkening of the lens formingcomposition may also prevent non-ultraviolet activating light frompenetrating the composition. This darkening effect may preventactivating light of any wavelength from initiating the polymerizationreaction throughout the lens forming composition.

When the light absorbing compounds absorb in the ultraviolet regionactivating light having a wavelength above about 380 nm may be used toprevent the darkening effect. Because the wavelength of the activatinglight is substantially above the wavelength at which the ultravioletlight absorbing compounds absorb, the darkening effect may be avoided.Additionally, activating light with a wavelength above about 380 nm maybe used to initiate the polymerization of the lens forming material. Bythe use of such activating light an eyeglass lens containing ultravioletlight absorbing compounds may, in some circumstances, be formed withoutthe use of a co-initiator.

In an embodiment the above-described lens forming composition, where thelight absorbing compound absorbs ultraviolet light, may be treated withactivating light having a wavelength above about 380 nm to activate thephotoinitiator. Preferably activating light having a wavelengthsubstantially between about 380 nm to 490 nm is used. By usingactivating light above about 380 nm the darkening effect caused by theultraviolet absorbing compounds may be avoided. The activating light maypenetrate into the lens forming composition, initiating thepolymerization reaction throughout the composition. A filter whichblocks light having a wavelength that is substantially below about 380nm may be used to prevent the ultraviolet absorbing compounds fromdarkening.

The use of activating light permits polymerization of the lens formingcomposition to proceed through the depths of the lens cavity. A cured,clear, aberration free lens is preferably formed in less than about30-60 minutes, more preferably in less than about 20 minutes. As usedherein a “clear lens” means a lens that transmits visible light withoutscattering so that objects beyond the lens are seen clearly. As usedherein “aberration” means the failure of a lens to producepoint-to-point correspondence between an object and its image. The lens,when exposed to ultraviolet light, preferably inhibits at least aportion of the ultraviolet light from being transmitted through thelens. In this manner the eye may be protected from certain light. A lensthat permits no ultraviolet light from passing through the lens (atleast with respect to certain UV wavelengths) is more preferred.

In an embodiment, the lens forming composition which contains anultraviolet absorbing compound may be cured with an activating light.Preferably, the activating light has a wavelength substantially aboveabout 380 nm. Activating lights may replace the ultraviolet lightswithin the UVEXS curing apparatus previously described herein anddepicted in FIG. 10. In another embodiment, the lens forming compositionmay be cured with activating light supplied from the FC-104 curingchamber which is depicted in FIGS. 14 and 15. The lens formingcomposition may be cured by exposing the composition to activating lightmultiple times using both the UVEXS and the FC-104. Alternatively, thelens forming composition may be cured by exposing the composition to aplurality of activating light pulses, at least one of the pulses havinga duration of less than about one second (more preferably less thanabout 0.1 seconds, and more preferably between 0.1 and 0.001 seconds).Preferably, all activating light directed toward the mold members is ata wavelength between about 380 nm to 490 nm. The previously describedembodiments which describe various methods and compositions for formingeyeglass lenses may also be utilized to form the eyeglass lens hereof,by replacing the ultraviolet light in these examples with activatinglight having a wavelength substantially greater than about 380 nm.

In an embodiment, the activating light may be generated from afluorescent lamp. The fluorescent lamp is preferably used to directactivating light rays toward at least one of the mold members. At leastone and preferably two fluorescent light sources, with strong emissionspectra in the 380 to 490 nm region may be used. When two light sourcesare used, they are preferably positioned on opposite sides of the moldcavity. A fluorescent lamp emitting activating light with the describedwavelengths is commercially available from Voltarc, Inc. of Fairfield,Conn. as model F20 T12/AQA/BP/65W.

Preferably three or four fluorescent lamps are positioned to providesubstantially uniform radiation over the entire surface of the moldassembly to be cured. The activating light source may be turned on andoff quickly between exposures. A flasher ballast may be used for thisfunction. A flasher ballast may operate in a standby mode wherein a lowcurrent is supplied to the lamp filaments to keep the filaments warm andthereby reduce the strike time of the lamp. Such a ballast iscommercially available from Magnatek, Inc of Bridgeport, Conn.Alternately, the light source may employ a shutter system to block thelight between doses. This shutter system is preferably controlled by amicro-processor based control system in order to provide the necessarydoses of light. A feedback loop may be used to control the lightintensity so that intensity fluctuations due to environmental variables(e.g. lamp temperature) and lamp aging are minimized. A light sensor maybe incorporated into the control system to minimize variances in dosefor a given exposure time.

The identity of the major polymerizable components of the lens formingcomposition tends to affect the optimal curing process. It isanticipated that the identity of the light absorbing compound present inthe monomer or blend of monomers may affect the optimal photoinitiatorsystem used as well as the optimal curing process used to initiatepolymerization. Also, varying the identities or the proportions of themonomer(s) in the lens forming composition may require adjustments tovarious production process variables including, but not limited to,exposure times, exposure intensities, cooling times and temperatures,postcure procedures and the like. For example, compositions includingrelatively slow reacting monomers, such as bisphenol A bis allylcarbonate or hexanediol dimethacrylate, or compositions includingrelatively higher proportions of such monomers may require either longerexposure times, higher intensities, or both. It is postulated thatincreasing the amount of either fast reacting monomer or the initiatorlevels present in a system will require reduced exposure times, morerigidly controlled light doses, and more efficient exothermic heatremoval.

Preferably, the monomers selected as components of the lens formingcomposition are capable of dissolving the light absorbing compoundsadded to them. As used herein “dissolving” means being substantiallyhomogeneously mixed. For example, monomers may be selected from a groupincluding polyol (allyl carbonate) monomers, multi-functional acrylatemonomers, and multi-functional methacrylic monomers for use in anultraviolet light absorbing lens forming composition.

In an embodiment, the mixture of monomers, previously described asPRO-629, may be blended together before addition of other componentsrequired to make the lens forming composition. This blend of monomers ispreferably used as the basis for a lens forming composition to whichultraviolet light absorbing compounds are added.

A polymerization inhibitor may be added to the monomer mixture atrelatively low levels to inhibit polymerization of the monomer atinappropriate times (e.g., during storage). Preferably about 0 to 50 ppmof monomethylether hydroquinone (MEHQ) are added to the monomer mixture.It is also preferred that the acidity of the monomer mixture be as lowas possible. Preferably less than about 100 ppm residual acrylic acidexists in the mixture. It is also preferred that the water content ofthe monomer mixture be relatively low, preferably less than about 0.15percent.

Photoinitiators which have utility in the present invention have beendescribed in previous embodiments. Ultraviolet light absorbing compoundswhich may be added to a normally ultraviolet transmissible lens formingcomposition have also been described in previous embodiments. Thequantity of photochromic pigments present in the lens formingcomposition is preferably sufficient to provide observable photochromiceffect. The amount of photochromic pigments present in the lens formingcomposition may widely range from about 1 ppm by weight to 1-5% byweight. In preferred compositions the photochromic pigments are presentin ranges from about 30 ppm to 2000 ppm. In the more preferredcompositions the photochromic pigments are present in ranges from about150 ppm to 1000 ppm. The concentration may be adjusted depending uponthe thickness of the lens being produced to obtain optimal visible lightabsorption characteristics.

In another embodiment co-initiators may be added to the lens formingcomposition. As described previously, such compositions may aid thepolymerization of the lens forming composition by interacting with thephotoinitiator such that the composition polymerizes in a substantiallyuniform manner. It is anticipated that the optimal amounts of the lensforming composition components is where the total amount of bothinitiators are minimized subject to the constraint of completepolymerization and production of a rigid, aberration free lens. Therelative proportions of the photoinitiator to the co-initiator may beoptimized by experimentation. For example, an ultraviolet absorptivelens forming composition that includes a photoinitiator with noco-initiator may be cured. If waves and distortions are observed in theresulting lens, a co-initiator may then be added to the lens formingcomposition by increasing amounts until a lens having the best opticalproperties is formed. It is anticipated that excess co-initiator in thelens forming composition should be avoided to inhibit problems of toorapid polymerization, yellowing of the lens, and migration of residual,unreacted co-initiator to the surface of the finished lens.

In an embodiment, hindered amine light stabilizers may be added to thelens forming composition. It is believed that these materials act toreduce the rate of degradation of the cured polymer caused by exposureto ultraviolet light by deactivating harmful polymer radicals. Thesecompounds may be effective in terminating oxygen and carbon freeradicals, and thus interfering with the different stages ofauto-oxidation and photo-degradation. Preferably, more than one monomerand more than one initiator are used in a lens forming composition toensure that the initial polymerization of the lens forming compositionwith activating light does not occur over too short a period of time.The use of such a lens forming composition may allow greater controlover the gel formation, resulting in better control of the opticalquality of the lens. Further, greater control over the rate ofexothermic heat generation may be achieved. Thus, cracking of the lensand premature release of the lens from the mold which are typicallycaused by the release of heat may be prevented. As mentioned above,exothermic reactions occur during the curing process of the lens formingcomposition. As previously described a “donut effect” may occur forpositive lens in which the relatively thin outer portion of the lensforming composition reaches its fully cured state before the relativelythick inner portion of the lens forming composition. Conversely, in anegative lens the relatively thin inner portion of the lens formingcomposition may reach its filly cured state before the relatively thickouter portion of the lens forming composition.

Accordingly, it is preferred that a greater amount of activating lightis applied to the thicker sections of the composition than to thethinner sections. In one embodiment, as shown in FIG. 36, the thicknessof a filter preferably varies so that a thinner section of the filtercorresponds to an adjacent thicker section of the mold cavity and athicker section of the filter corresponds to an adjacent thinner sectionof the mold cavity. In other words, the thickness of the filter may bevaried according to the varying thickness of the lens formingcomposition disposed within the mold cavity. The filter is preferably ahazy filter that may be formed by a variety of means. The filter may bepolymerized from a hazy material or any combination of materials whichcreate haze. More specifically, the filter may be a “lens” (i.e., apiece of plastic shaped like a lens) made by adding an incompatiblechemical to a typical lens forming composition. For example, a bisphenolcompound may be added to a lens forming composition and polymerized,resulting in a cloudy filter in the shape of a lens that separates lightinto numerous (e.g., millions) of fragments. The filter may be injectionmolded from polyethylene or any suitable thermoplastic.

In one embodiment, after the lens forming composition has been placed inthe mold cavity, it may be pre-cooled 3 to 7 minutes before beingexposed to activating light. Thus, the lens forming composition may becooled to below ambient temperature prior to polymerization of the lensforming composition. Advantageously, the heat released by the reactionwithin the composition may be balanced by the coolness of thecomposition so that the composition is not exposed to extreme amounts ofthermal radiation. Thus, exposing the lens forming composition to belowambient temperatures before the reaction is initiated may inhibitundesirable effects resulting from the exothermic nature of thereaction. For example, cooling the lens forming composition might helpprevent the loss of process control caused by variations in the rate ofreaction that result from temperature changes of the lens formingcomposition.

In an embodiment, the activating light is directed toward the moldmembers until at least a portion of the lens forming composition is agel. At this point, application of the activating light is preferablyterminated to inhibit the polymerization reaction from proceeding toorapidly, thereby inhibiting the rate of heat generation from increasingso rapidly that premature release of the lens from the mold cavityand/or cracking of the lens results. The heat generated by thepolymerization reaction may also be controlled by applying a stream ofair to the mold cavity to remove heat from he mold cavity. Cooling ofthe mold cavity has been previously described. After termination of theactivating light, the gasket holding the two mold members together ispreferably removed to expose the lens forming composition to air whilethe reaction is allowed to continue at a desired rate. The air mayadvantageously help cool the lens forming composition. In an embodiment,the lens forming composition may be exposed to ambient conditions forabout 5 to 30 minutes, depending on the mass of the composition. It isbelieved that approximately one minute of such exposure is preferred foreach gram of the composition. Since the amount of heat released duringreaction tends to be proportional to the mass of the composition, themore mass the composition has, the longer it may be cooled. Aftercooling the composition, it may be exposed to activating light again ifdesired.

In an embodiment, the inner surface, i.e., the casting face, of thefront mold member may be coated with one or more hardcoat layers beforethe lens forming composition is placed within the mold cavity.Preferably, two hardcoat layers are used so that any imperfections, suchas pin holes in the first hardcoat layer, are covered by:the secondhardcoat layer. The resulting double hardcoat layer is preferablyscratch resistant and protects the subsequently formed eyeglass lens towhich the double hardcoat layer adheres. In an embodiment, the castingface of the back mold member may be coated with a material prior tofilling the mold cavity with the lens forming composition. This materialmay be capable of being tinted with dye. This tintable coat preferablyadheres to the lens forming composition so that dyes may later be addedto the resulting eyeglass lens for tinting the lens.

In an embodiment, dyes may be added to the lens forming composition. Itis believed that certain dyes may be used to attack and encapsulateambient oxygen so that the oxygen cannot react with free radicals formedduring the curing process. Also, dyes may be added to the composition toalter the color of an inactivated photochromic lens. For instance, ayellow color that sometimes results after a lens is formed may be“hidden” if a blue-red or blue-pink dye is present in the lens formingcomposition. The inactivated color of a photochromic lens may also beadjusted by the addition of non-photochromic pigments to the lensforming composition.

In an embodiment, the eyeglass lens that is formed may be coated with ahydrophobic layer, e.g. a hardcoat layer. The hydrophobic layerpreferably extends the life of the photochromic pigments near thesurfaces of the lens by preventing water and oxygen molecules fromdegrading the photochromic pigments.

In a preferred embodiment, both mold members are coated with a curedadhesion-promoting composition prior to placing the lens formingcomposition into the mold cavity. Providing the mold members with suchan adhesion-promoting composition is preferred to increase the adhesionbetween the casting surface of the mold and the lens formingcomposition. The adhesion-promoting composition thus reduces thepossibility of premature release of the lens from the mold. Further, itis believed that such a coating also provides an oxygen and moisturebarrier on the lens which serves to protect the photochromic pigmentsnear the surface of the lens from oxygen and moisture degradation. Yetfurther, the coating provides abrasion resistance, chemical resistance,and improved cosmetics to the finished lens.

An eyeglass lens formed using the lens forming composition of thepresent invention is not only applicable for use as a prescription lensand may be used for a non-prescription lens as well. Particularly, sucha lens may be used in sunglasses. Advantageously, photochromic sunglasslenses would remain light enough in color to allow a user to see throughthem clearly while at the same time prohibiting ultraviolet light frompassing through the lenses. In one embodiment, a background dye may beadded to the photochromic lens to make the lens appear to be a darkshade of color at all times like typical sunglasses.

Each of the embodiments described above may be combined or usedindividually.

Preparing Lens of Various Powers by Altering the Lens FormingConditions.

It has been determined that in some embodiments the finished power of anactivating light polymerized lens may be controlled by manipulating thecuring temperature of the lens forming composition. For instance, for anidentical combination of mold members and gasket, the focusing power ofthe produced lens may be increased or decreased by changing theintensity of activating light across the lens mold cavity or the facesof the opposed mold members.

As the lens forming material begins to cure, it passes through a gelstate, the pattern of which, within the lens cell, leads to the properdistribution of internal stresses generated later in the cure when thelens forming material begins to shrink. As the lens forming materialshrinks during the cure, the opposed mold members will preferably flexas a result of the different amounts of shrinkage between the relativelythick and the relatively thin portions of the lens. When a negativelens, for example, is cured, the upper or back mold member willpreferably flatten and the lower or front mold member will preferablysteepen with most of the flexing occurring in the lower or front moldmember. Conversely, with a positive lens, the upper or back mold memberwill preferably steepen and the lower or front mold member willpreferably flatten with most of the flexing occurring in the upper orback mold member.

By varying the intensity of the activating light between the relativelythin and the relatively thick portions of the lens in the lens formingcavity, it is possible to create more or less total flexing. Those lightconditions which result in less flexing will tend to minimize thepossibility of premature release.

The initial curvature of the opposed mold members and the centerthickness of the lens produced can be used to compute the targeted powerof the lens. Herein, the “targeted power” of a lens is the power a lensmay have if the lens were to have a curvature and thicknesssubstantially identical to the mold cavity formed by the opposed moldmembers. The activating light conditions may be manipulated to alter thepower of the lens to be more or less than the targeted power.

By varying the amount of activating light reaching the lens mold thepolymerization rate, and therefore the temperature of the lens formingcomposition may be controlled. It has been determined that the maximumtemperature reached by the lens forming composition during and/or afteractivation by light may effect the final power of the lens. By allowingthe lens forming composition to reach a temperature higher than thetypical temperatures described in previous embodiments, but less thanthe temperature at which the formed lens will crack, the power of thelens may be decreased. Similarly, controlling the polymerization suchthat the temperature of the lens forming composition remainssubstantially below the typical temperatures described in previousembodiments, but at a sufficient temperature such that a properly curedlens is formed, the power of the lens may be increased. Similarly,increasing such lens forming composition temperature during curing maydecrease the power of the resulting lens.

In an embodiment, an ophthalmic eyeglass lens may be made from a lensforming composition comprising a monomer and a photoinitiator, byirradiation of the lens forming composition with activating light. Thecomposition may optionally include one or more of: an ultravioletabsorbing compound, a polymerization inhibitor, a co-initiator, ahindered amine light stabilizer, and a dye. The activating light mayinclude ultraviolet, visible or infrared light. The lens formingcomposition may be treated with activating light such that an eyeglassis formed which has a power substantially equal to the targeted powerfor a given mold cavity. The peak temperature of the lens formingprocess may be the maximum temperature attained after the application ofeach pulse of activating light. As depicted in FIG. 40, each pulse ofactivating light may cause the lens forming composition to rise to apeak temperature.

After reaching this peak temperature the lens forming composition maybegin to cool until the next application of activating light. If thepeak temperature of the lens forming composition is controlled such thatthe formed lens has a power substantially equal to the targeted power,the peak temperature is referred to as the “matching temperature”. Thematching temperature may be determined by performing a series ofexperiments using the same mold cavity. In these experiments the peaktemperature attained during the process is preferably varied. Bymeasuring the power of the lenses obtained through this experiment thematching temperature range may be determined.

When the temperature of the lens forming composition is allowed to riseabove the matching temperature during treatment with activating light,the power of the lens may be substantially less than the targeted powerof the lens. Alternatively, when the temperature of the lens formingcomposition is allowed to remain below the matching temperature, thepower of the lens may be substantially greater than the targeted powerof the lens. In this manner, a variety of lenses having substantiallydifferent lens powers from the targeted power may be produced from thesame mold cavity.

When the lenses cured by the activating light are removed from theopposed mold members, they are typically under a stressed condition. Ithas been determined that the power of the lens can be brought to a finalresting power, by subjecting the lenses to a post-curing heat treatmentto relieve the internal stresses developed during the cure and cause thecurvature of the front and the back of the lens to shift. Typically, thelenses are cured by the activating light in about 10-30 minutes(preferably about 15 minutes). The post-curing heat treatment isconducted at approximately 85-120° C. for approximately 5-15 minutes.Preferably, the post-curing heat treatment is conducted at 100-110° C.for approximately 10 minutes. Prior to the post-cure, the lensesgenerally have a lower power than the final resting power. Thepost-curing heat treatment reduces yellowing of the lens and reducesstress in the lens to alter the power thereof to a final resting power.The post-curing heat treatment can be conducted in a conventionalconvection oven or any other suitable device.

In an embodiment, an ophthalmic eyeglass lens may be made from a lensforming composition comprising a monomer and a photoinitiator, byirradiation of the lens forming composition with activating light. Thecomposition may optionally include one or more of: an ultravioletabsorbing compound, a polymerization inhibitor, a co-initiator, ahindered amine light stabilizer, and a dye. The activating light mayinclude ultraviolet, visible or infrared light. The lens formingcomposition may be treated with activating light such that an eyeglassis formed. The lens may be kept within the mold cavity formed by themold members until the light has completely cured the lens formingcomposition. The minimum time which a lens must remain in the moldcavity to produce a lens with the targeted power, with respect to themold cavity, is herein referred to as the “demolding time”. Thedemolding time may be determined by performing a series of experimentsusing the same mold cavity. In these experiments the time that the lensis released from the mold cavity during the process is preferablyvaried. By measuring the power of the lenses obtained through thisexperiment the demolding time range may be determined.

When a formed lens is removed prior to the demolding time, the power ofthe lens may be substantially greater than the targeted power of thelens. By varying the demolding time a variety of lenses havingsubstantially greater lens powers from the targeted power may beproduced from the same mold cavity.

Microprocessor Based Control System

In an embodiment a lens curing apparatus may include a microprocessorbased control system. The control system may perform some and/or all ofa number of functions during the lens curing process, including: (i)measuring the ambient room temperature; (ii) determining the initialdose of light required to cure the lens forming composition, based onthe ambient room temperature; (iii) applying the activating light withan intensity and duration sufficient to equal the determined dose; (iv)measuring the composition's temperature response during and subsequentto the application of the first dose of light; (v) calculating the doserequired for the next application of activating light; (vi) applying theactivating light with an intensity and duration sufficient to equal thedetermined second dose; (vii) repeating these procedures until the lensforming material is substantially cured; (viii) determining when thecuring process is complete by monitoring the temperature response of thelens forming composition during the application of activating light;(ix) tracking the usage and maintenance requirements of the system.Herein, “dose” refers to the amount of light energy applied to anobject, the energy of the incident light being determined by theintensity and duration of the light.

A temperature monitor may be located at a number of positions within amold chamber. Mold chambers including a temperature monitor have beendescribed in the previous embodiments. In one embodiment an infra-redtemperature sensor may be located such that it can measure thetemperature of the mold and/or the lens forming composition in the moldcavity. One infra-red temperature sensor may be the Cole-Parmer ModelE39669-00 (Vernon Hills, Ill.).

The temperature monitor may measure the temperature within the chamberand/or the temperature of air exiting the chamber. The controller may beadapted to send a signal to a cooler and/or distributor to vary theamount and/or temperature of the cooling air. The temperature monitormay also determine the temperature at any of a number of locationsproximate the mold cavity. The temperature monitor preferably sends asignal to the controller such that the temperature of mold cavity and/orthe lens forming composition is known by the controller throughout thecuring process.

During the initial set-up the temperature of the lens formingcomposition within the mold cavity is determined. This initialtemperature of the lens forming composition may be about equal to theambient room temperature. The controller may then determine the initialtemperature of the lens forming composition by measuring the ambientroom temperature. Alternatively, the initial temperature of the lensforming composition may be measured directly using the aforementionedtemperature sensors.

The controller preferably determines the initial dose to be given to thelens forming composition based on the initial temperature of thecomposition. The controller may use a table to determine the initialdose, the table including a series of values correlating the initialtemperature to the initial dose and/or the mass of the lens formingcomposition. The table may be prepared by routine experimentation. Toprepare the table a specific lens forming composition of a specific massis preferably treated with a known dose of activating light. The moldcavity is preferably disassembled and the gellation pattern of the lensforming composition observed. This procedure may be repeated, increasingor decreasing the dosage as dictated by the gellation patterns, untilthe optimal dosage is determined for the specific lens formingcomposition.

During this testing procedure the initial temperature of the lensforming composition may be determined, this temperature-being hereinreferred to as the “testing temperature”. In this manner the optimaldose for the lens forming composition at the testing temperature may bedetermined. When the lens forming material has an initial temperaturethat is substantially equal to the testing temperature, the initialdosage may be substantially equal to the experimentally determineddosage. When the lens forming material has a temperature that issubstantially greater or less than the testing temperature, the initialdose may be calculated based on a function of the experimentallydetermined initial dose.

In an embodiment, the controller is adapted to control the intensity andduration of activating light pulses delivered from the activating lightsource and the time interval between the pulses. The activating lightsource may include a capacitor which stores the energy required todeliver the pulses of activating light. The capacitor may be adapted toallow pulses of activating light to be delivered as frequently asdesired. A light sensor may be used to determine the intensity ofactivating light emanating from the source. The light sensor ispreferably adapted to send a signal to the controller, which ispreferably adapted to maintain the intensity of the activating light ata selected level. A filter may be positioned between the activatinglight source and the light sensor and is preferably adapted to inhibit aportion of the activating light rays from contacting the light sensor.This filter may be necessary to keep the intensity of the activatinglight upon the light sensor within the detectable range of the lightsensor.

In an embodiment, a shutter system is used to control the application ofactivating light rays to the lens forming material. The shutter systempreferably includes air-actuated shutter plates that may be insertedinto the curing chamber to prevent activating light from reaching thelens forming material. The shutter system may be coupled to thecontroller, which may actuate an air cylinder to cause the shutterplates to be inserted or extracted from the curing chamber. Thecontroller preferably allows the insertion and extraction of the shutterplates at specified time intervals. The controller may receive signalsfrom temperature sensors allowing the time intervals in which theshutters are inserted and/or extracted to be adjusted as a function of atemperature of the lens forming composition and/or the molds. Thetemperature sensor may be located at numerous positions proximate themold cavity and/or casting chamber.

In an embodiment a single dose of activating light may be used to cure alens forming composition. The controller may monitor the change intemperature of the lens forming composition during the application ofactivating light. The activating light preferably initiates apolymerization reaction such that the temperature of the lens formingcomposition begins to rise. By monitoring the change in temperature overa time period the controller may determine the rate of temperaturechange. The controller preferably controls the polymerization of thelens forming composition based on the rate of temperature change. Whenthe temperature is found to be rising at a faster than desired rate, thedesired rate being determined based on previous experiments, thetemperature controller may alter the intensity or duration of the pulsesuch that the rate of temperature change is lowered. Typically theduration of the activating light is shortened and/or the intensity ofthe activating light is diminished to achieve this effect. Thecontroller may also increase the rate of cooling air blowing across themold to help lower the temperature of the lens forming composition.Alternatively, if the temperature of the reaction is increasing tooslowly, the controller may increase the intensity of the activatinglight and/or increase the duration of the pulse. Additionally, thecontroller may decrease the rate of cooling air blowing across the moldto allow the temperature of the lens forming composition to rise at afaster rate.

One manner in which the temperature may be controlled is by monitoringthe temperature during the application of activating light, as describedin U.S. Pat. No. 5,422,046 to Tarshiani, et al. During activating lightirradiation the temperature of the lens forming composition tends torise. When the temperature reaches a predetermined upper set point theactivating light source is preferably turned off. Removal of theactivating energy may allow the temperature to gradually begin to fall.When the temperature is reduced to a predetermined lower set point theactivating light source is turned on. In this way the temperature may becontrolled within a desired range. This temperature range tends to bevery broad due to the nature of the lens forming polymerizationreactions. For example, turning the activating light off at apredetermined upper set point may not insure that the temperature of thelens forming composition will stop at that point. In fact, it is morelikely that the temperature may continue to rise after the upper setpoint has been reached. To offset this effect the upper set point may beset at a temperature lower than the upper temperature desired during thelens forming process. Such a method of temperature control may beinsufficient to control the temperature. As shown in FIG. 40, increasein the temperature of a lens forming composition during the lens formingprocess may not be constant. Since the increase in temperature of thecomposition changes as the process continues, the use of an upper setpoint for controlling the temperature may not adequately prevent thecomposition from reaching greater than desired temperatures.Additionally, near the completion of the process the upper set point maybe set too low, thereby preventing the lens forming composition fromreaching a temperature that is adequate to maintain the polymerizationreaction due to insufficient doses of activating light.

In an embodiment the temperature control process may be described as amodified PID (Proportional, Integral, Derivative) control schema.Preferably the temperature of the lens forming composition is controlledin this manner with a PID controller. The PID controller may use anumber of factors to determine the dose of activating light applied foreach pulse. The PID controller preferably measures the temperature aswell as the rate of temperature change.

The PID controller uses a method involving the combination ofproportional, integral and derivative controlling methods. The first,proportional control, may be achieved by mixing two control factors insuch a way as to achieve the desired effect. For lens control the twofactors which may have the most effect on temperature control are thedosage of activating light and the flow rate of the cooling air. Thesetwo factors may be altered to achieve a desired temperature response. Ifthe temperature must be raised as rapidly as possible a full dosage oflight may delivered with no cooling air present. Similarly, if thecomposition must be rapidly cooled the sample may be treated withcooling air only. Preferably the two factors, application of incidentlight and cooling, are both applied to achieve the desired temperatureresponse. The mixture, or proportions of these factors may allow thetemperature of the composition to be controlled.

The use of proportional control tends to ignore other effects thatinfluence the temperature of the lens forming composition. During thelens forming process the temperature of the lens forming composition mayvary due to the rate of polymerization of the reaction. When thecomposition is undergoing a rapid rate of polymerization, thetemperature of the composition may rise beyond that determined by theproportional setting of the activating light and cooling air controls.Toward the end of the process the lens may become too cool due to the areduction in the rate of polymerization of the composition. The use ofproportional control may therefore be inadequate to control thisprocedure and may lead to greater than desired variations in thetemperature of the composition.

These limitations may be overcome by altering the proportions of the twocomponents in response to the temperature of the composition. A singleset point may be used to control the temperature of a reaction. As thetemperature rises above this set point the proportion of the activatinglight and cooling may be adjusted such that the temperature begins tolower back toward the set point. If the temperature drops below the setpoint the proportion of activating light and cooling may be adjusted toraise the temperature back to the set point. Typically, to lower thetemperature the dose of activating light may be reduced and/or the flowrate of the cooling air may be increased. To raise the temperature thedose of activating light may be increased and/or the flow rate of thecooling air may be decreased.

The use of proportional control in this manner may not lead to a steadytemperature. Depending on the set point and the response time of thelens forming composition to variations in the dosage of light and/orcooling air, the temperature may oscillate over the set point, neverattaining a steady value. To better control such a system the rate ofchange of the temperature over a predetermined time period is preferablymonitored. As the temperature rises the rate at which the temperaturerises is preferably noted. Based on this rate of change the controllercan then alter the dosage of activating light and/or cooling air suchthat a temperature much closer to the set point may be achieved. Sincethe rate will change in response to changes in the rate ofpolymerization, such a system may better control the temperature of thelens forming composition throughout the process.

In an embodiment the controller is a modified PID controller. Thecontroller preferably monitors the temperature of the lens formingcomposition throughout the process. Additionally, the controller maymonitor the rate of change of temperature throughout the reaction. Whena plurality of pulses are being applied to control the polymerization,the controller preferably controls the duration and intensity of eachpulse to control the temperature of the composition. In a typicalprocess the rate of change in temperature is preferably monitored afterthe application of an activating light pulse. If the temperature istrending in an upward direction, the controller preferably waits for thetemperature to crest and start descending, before the application ofadditional light pulses. This cresting temperature may vary, as depictedin FIG. 40, throughout the lens forming process. After the temperaturehas passed a predetermined set point, a dose, calculated from the rateof change in temperature caused by the application of the previouspulse, is applied to the lens forming composition. After the light pulseis delivered the controller repeats the procedure.

When the reaction nears completion the controller detects the lack ofresponse to the last exposure (i.e. the lens temperature did notincrease appreciably). At this point the controller may apply a finaldose to assure a substantially complete cure and notify the operatorthat the mold assembly is ready to be removed form the chamber.Additionally, The microprocessor based control system provides systemdiagnostics and manages an interlock system for safety purposes. Thecontrol system will notify the user when routine maintenance is due orwhen a system error is detected. The control system will track systemusage and lens yield rates.

It is to be understood that embodiments of a microprocessor basedcontrol system, as described above, may be combined with the methods andapparatus of preferred embodiments described above in the previoussections.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements and compositionsdescribed herein or in the features or in the sequence of features ofthe methods described herein without departing from the spirit and scopeof the invention as described in the following claims.

1. A lens forming composition, comprising; a monomer; a photoinitiatorthat activates a co-initiator after being exposed to at least a portionof activating light during curing, wherein the co-initiator activatescuring of the monomer to form the eyeglass lens, and wherein theco-initiator comprises an acrylyl amine; and a photochromic compound;and wherein the lens forming composition is curable by exposure toactivating light having a wavelength below 400 nm to form asubstantially clear and aberration free eyeglass lens in a time periodof less than about 10 minutes.
 2. The composition of claim 1, whereinthe acrylyl amine is selected from the group consisting of monoacrylatedamines, diacrylated amines, or mixtures thereof.
 3. The composition ofclaim 1, wherein an amount of the co-initiator in the lens formingcomposition ranges from about 1 ppm to about 7% by weight.
 4. Thecomposition of claim 1, wherein the photoinitiator comprisesbis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphine oxide, or amixture of bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphineoxide and 1-hydroxycyclohexylphenylketone.
 5. The composition of claim1, wherein the photoinitiator comprises an acylphosphine oxide.
 6. Thecomposition of claim 1, wherein the photoinitiator comprises1-hydroxycyclohexylphenylketone,bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl)phosphine oxide,mixtures of bis(2,6-dimethoxybenzoyl)-(2,4,4,-trimethylpentyl)-phosphineoxide and 2-hydroxy-2-methyl-1-phenylpropan-1-one, mixtures of(2,6-dimethoxybenzoyl)-(2,4,4,-trimethylpentyl)phosphine oxide and1-hydroxycyclohexylphenylketone, 2,2-dimethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, mixtures of2,4,6-trimethylbenzoyldiphenylphosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one, 2,2-diethoxyacetophenone,benzil dimethyl ketal, α-hydroxy ketone, 2-methylthioxanthone,2-chlorothioxanthone, thioxanthone, xanthone, 2-isopropylthioxanthone,mixtures of triaryl sulfonium hexafluoroantimonate and propylenecarbonate, diaryl diodonium hexafluoroantimonate, mixtures ofbenzophenone and 1-hydroxycyclohexylphenylketone,2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-1-butanone,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,bis(η5-2,4-cyclopentadien-1-yl)-bis-[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl]titanium,mixtures of 2,4,6-trimethyl benzophenone and 4-methylbenzophenone,benzoyl peroxide, methyl benzoyl formate, or mixtures thereof.
 7. Thecomposition of claim 1, wherein the photochromic compound comprises oneor more spiropyrans.
 8. The composition of claim 1, wherein thephotochromic compound comprises one or more spirooxazines.
 9. Thecomposition of claim 1, wherein the photochromic compound comprises oneor more spiropyrans and one or more spirooxazines.
 10. The compositionof claim 1, wherein the photochromic compound comprises one or morespironaphthoxazines, one or more spiropyridobenzoxazines, one or morespirobenzoxazines, one or more naphthopyrans, one or more benzopyrans,one or more spironaphthopyrans, one or more indolinospironaphthoxazines,one or more indolinospironaphthopyrans, one or more diarylnaphthopyrans,or mixtures thereof.
 11. The composition of claim 1, wherein an amountof photochromic compound in the lens forming composition ranges fromabout 1 ppm to about 5% by weight.
 12. The composition of claim 1,further comprising a hindered phenolic compound, the hindered phenoliccompound comprisingthiodiethylene-bis-(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate oroctadecyl-3,5-bis-(1,1-dimethylethyl)-4-hydroxybenzenepropanoate forinhibiting oxidation of the lens forming composition.
 13. Thecomposition of claim 1, wherein the monomer is apolyethylenic-functional monomer containing ethylenically unsaturatedgroups selected from acrylyl and methacrylyl.
 14. The composition ofclaim 1, wherein the monomer comprises tripropyleneglycol diacrylate,tetraethyleneglycol diacrylate, trimethylolpropane triacrylate,hexanediol dimethacrylate, or mixtures thereof.
 15. The composition ofclaim 1, further comprising a dye.
 16. The composition of claim 1,wherein the lens forming composition is curable by exposure toactivating light comprising a wavelength below 400 nm to form asubstantially clear and aberration free eyeglass lens in a time periodof less than about 10 minutes.
 17. The composition of claim 1, whereinthe photochromic compound substantially absorbs light having awavelength of less than 380 nm.